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<link rel="StyleSheet" href="CQL.css" type="text/css" media="screen">
h1. Cassandra Query Language (CQL) v3.1.4
<span id="tableOfContents">
{toc:maxLevel=3}
</span>
h2. CQL Syntax
h3. Preamble
This document describes the Cassandra Query Language (CQL) version 3. CQL v3 is not backward compatible with CQL v2 and differs from it in numerous ways. Note that this document describes the last version of the languages. However, the "changes":#changes section provides the diff between the different versions of CQL v3.
CQL v3 offers a model very close to SQL in the sense that data is put in _tables_ containing _rows_ of _columns_. For that reason, when used in this document, these terms (tables, rows and columns) have the same definition than they have in SQL. But please note that as such, they do *not* refer to the concept of rows and columns found in the internal implementation of Cassandra and in the thrift and CQL v2 API.
h3. Conventions
To aid in specifying the CQL syntax, we will use the following conventions in this document:
* Language rules will be given in a "BNF":http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form -like notation:
bc(syntax). <start> ::= TERMINAL <non-terminal1> <non-terminal1>
* Nonterminal symbols will have @<angle brackets>@.
* As additional shortcut notations to BNF, we'll use traditional regular expression's symbols (@?@, @+@ and @*@) to signify that a given symbol is optional and/or can be repeated. We'll also allow parentheses to group symbols and the @[<characters>]@ notation to represent any one of @<characters>@.
* The grammar is provided for documentation purposes and leave some minor details out. For instance, the last column definition in a @CREATE TABLE@ statement is optional but supported if present even though the provided grammar in this document suggest it is not supported.
* Sample code will be provided in a code block:
bc(sample). SELECT sample_usage FROM cql;
* References to keywords or pieces of CQL code in running text will be shown in a @fixed-width font@.
h3(#identifiers). Identifiers and keywords
p. The CQL language uses _identifiers_ (or _names_) to identify tables, columns and other objects. An identifier is a token matching the regular expression @[a-zA-Z][a-zA-Z0-9_]@@*@.
p. A number of such identifiers, like @SELECT@ or @WITH@, are _keywords_. They have a fixed meaning for the language and most are reserved. The list of those keywords can be found in "Appendix A":#appendixA.
p. Identifiers and (unquoted) keywords are case insensitive. Thus @SELECT@ is the same than @select@ or @sElEcT@, and @myId@ is the same than @myid@ or @MYID@ for instance. A convention often used (in particular by the samples of this documentation) is to use upper case for keywords and lower case for other identifiers.
p. There is a second kind of identifiers called _quoted identifiers_ defined by enclosing an arbitrary sequence of characters in double-quotes(@"@). Quoted identifiers are never keywords. Thus @"select"@ is not a reserved keyword and can be used to refer to a column, while @select@ would raise a parse error. Also, contrarily to unquoted identifiers and keywords, quoted identifiers are case sensitive (@"My Quoted Id"@ is _different_ from @"my quoted id"@). A fully lowercase quoted identifier that matches @[a-zA-Z][a-zA-Z0-9_]@@*@ is equivalent to the unquoted identifier obtained by removing the double-quote (so @"myid"@ is equivalent to @myid@ and to @myId@ but different from @"myId"@). Inside a quoted identifier, the double-quote character can be repeated to escape it, so @"foo "" bar"@ is a valid identifier.
h3(#constants). Constants
CQL defines the following kind of _constants_: strings, integers, floats, booleans, uuids and blobs:
* A string constant is an arbitrary sequence of characters characters enclosed by single-quote(@'@). One can include a single-quote in a string by repeating it, e.g. @'It''s raining today'@. Those are not to be confused with quoted identifiers that use double-quotes.
* An integer constant is defined by @'-'?[0-9]+@.
* A float constant is defined by @'-'?[0-9]+('.'[0-9]*)?([eE][+-]?[0-9+])?@. On top of that, @NaN@ and @Infinity@ are also float constants.
* A boolean constant is either @true@ or @false@ up to case-insensitivity (i.e. @True@ is a valid boolean constant).
* A "UUID":http://en.wikipedia.org/wiki/Universally_unique_identifier constant is defined by @hex{8}-hex{4}-hex{4}-hex{4}-hex{12}@ where @hex@ is an hexadecimal character, e.g. @[0-9a-fA-F]@ and @{4}@ is the number of such characters.
* A blob constant is an hexadecimal number defined by @0[xX](hex)+@ where @hex@ is an hexadecimal character, e.g. @[0-9a-fA-F]@.
For how these constants are typed, see the "data types section":#types.
h3. Comments
A comment in CQL is a line beginning by either double dashes (@--@) or double slash (@//@).
Multi-line comments are also supported through enclosure within @/*@ and @*/@ (but nesting is not supported).
bc(sample).
-- This is a comment
// This is a comment too
/* This is
a multi-line comment */
h3(#statements). Statements
CQL consists of statements. As in SQL, these statements can be divided in 3 categories:
* Data definition statements, that allow to set and change the way data is stored.
* Data manipulation statements, that allow to change data
* Queries, to look up data
All statements end with a semicolon (@;@) but that semicolon can be omitted when dealing with a single statement. The supported statements are described in the following sections. When describing the grammar of said statements, we will reuse the non-terminal symbols defined below:
bc(syntax)..
<identifier> ::= any quoted or unquoted identifier, excluding reserved keywords
<tablename> ::= (<identifier> '.')? <identifier>
<string> ::= a string constant
<integer> ::= an integer constant
<float> ::= a float constant
<number> ::= <integer> | <float>
<uuid> ::= a uuid constant
<boolean> ::= a boolean constant
<hex> ::= a blob constant
<constant> ::= <string>
| <number>
| <uuid>
| <boolean>
| <hex>
<variable> ::= '?'
| ':' <identifier>
<term> ::= <constant>
| <collection-literal>
| <variable>
| <function> '(' (<term> (',' <term>)*)? ')'
<collection-literal> ::= <map-literal>
| <set-literal>
| <list-literal>
<map-literal> ::= '{' ( <term> ':' <term> ( ',' <term> ':' <term> )* )? '}'
<set-literal> ::= '{' ( <term> ( ',' <term> )* )? '}'
<list-literal> ::= '[' ( <term> ( ',' <term> )* )? ']'
<function> ::= <ident>
<properties> ::= <property> (AND <property>)*
<property> ::= <identifier> '=' ( <identifier> | <constant> | <map-literal> )
p.
Please note that not every possible productions of the grammar above will be valid in practice. Most notably, @<variable>@ and nested @<collection-literal>@ are currently not allowed inside @<collection-literal>@.
p. A @<variable>@ can be either anonymous (a question mark (@?@)) or named (an identifier preceded by @:@). Both declare a bind variables for "prepared statements":#preparedStatement. The only difference between an anymous and a named variable is that a named one will be easier to refer to (how exactly depends on the client driver used).
p. The @<properties>@ production is use by statement that create and alter keyspaces and tables. Each @<property>@ is either a _simple_ one, in which case it just has a value, or a _map_ one, in which case it's value is a map grouping sub-options. The following will refer to one or the other as the _kind_ (_simple_ or _map_) of the property.
p. A @<tablename>@ will be used to identify a table. This is an identifier representing the table name that can be preceded by a keyspace name. The keyspace name, if provided, allow to identify a table in another keyspace than the currently active one (the currently active keyspace is set through the <a href="#useStmt"><tt>USE</tt></a> statement).
p. For supported @<function>@, see the section on "functions":#functions.
h3(#preparedStatement). Prepared Statement
CQL supports _prepared statements_. Prepared statement is an optimization that allows to parse a query only once but execute it multiple times with different concrete values.
In a statement, each time a column value is expected (in the data manipulation and query statements), a @<variable>@ (see above) can be used instead. A statement with bind variables must then be _prepared_. Once it has been prepared, it can executed by providing concrete values for the bind variables. The exact procedure to prepare a statement and execute a prepared statement depends on the CQL driver used and is beyond the scope of this document.
h2(#dataDefinition). Data Definition
h3(#createKeyspaceStmt). CREATE KEYSPACE
__Syntax:__
bc(syntax)..
<create-keyspace-stmt> ::= CREATE KEYSPACE (IF NOT EXISTS)? <identifier> WITH <properties>
p.
__Sample:__
bc(sample)..
CREATE KEYSPACE Excelsior
WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3};
CREATE KEYSPACE Excalibur
WITH replication = {'class': 'NetworkTopologyStrategy', 'DC1' : 1, 'DC2' : 3}
AND durable_writes = false;
p.
The @CREATE KEYSPACE@ statement creates a new top-level _keyspace_. A keyspace is a namespace that defines a replication strategy and some options for a set of tables. Valid keyspaces names are identifiers composed exclusively of alphanumerical characters and whose length is lesser or equal to 32. Note that as identifiers, keyspace names are case insensitive: use a quoted identifier for case sensitive keyspace names.
The supported @<properties>@ for @CREATE KEYSPACE@ are:
|_. name |_. kind |_. mandatory |_. default |_. description|
|@replication@ | _map_ | yes | | The replication strategy and options to use for the keyspace. |
|@durable_writes@ | _simple_ | no | true | Whether to use the commit log for updates on this keyspace (disable this option at your own risk!). |
The @replication@ @<property>@ is mandatory. It must at least contains the @'class'@ sub-option which defines the replication strategy class to use. The rest of the sub-options depends on that replication strategy class. By default, Cassandra support the following @'class'@:
* @'SimpleStrategy'@: A simple strategy that defines a simple replication factor for the whole cluster. The only sub-options supported is @'replication_factor'@ to define that replication factor and is mandatory.
* @'NetworkTopologyStrategy'@: A replication strategy that allows to set the replication factor independently for each data-center. The rest of the sub-options are key-value pairs where each time the key is the name of a datacenter and the value the replication factor for that data-center.
* @'OldNetworkTopologyStrategy'@: A legacy replication strategy. You should avoid this strategy for new keyspaces and prefer @'NetworkTopologyStrategy'@.
Attempting to create an already existing keyspace will return an error unless the @IF NOT EXISTS@ option is used. If it is used, the statement will be a no-op if the keyspace already exists.
h3(#useStmt). USE
__Syntax:__
bc(syntax). <use-stmt> ::= USE <identifier>
__Sample:__
bc(sample). USE myApp;
The @USE@ statement takes an existing keyspace name as argument and set it as the per-connection current working keyspace. All subsequent keyspace-specific actions will be performed in the context of the selected keyspace, unless "otherwise specified":#statements, until another USE statement is issued or the connection terminates.
h3(#alterKeyspaceStmt). ALTER KEYSPACE
__Syntax:__
bc(syntax)..
<create-keyspace-stmt> ::= ALTER KEYSPACE <identifier> WITH <properties>
p.
__Sample:__
bc(sample)..
ALTER KEYSPACE Excelsior
WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 4};
p.
The @ALTER KEYSPACE@ statement alter the properties of an existing keyspace. The supported @<properties>@ are the same that for the "@CREATE TABLE@":#createKeyspaceStmt statement.
h3(#dropKeyspaceStmt). DROP KEYSPACE
__Syntax:__
bc(syntax). <drop-keyspace-stmt> ::= DROP KEYSPACE ( IF EXISTS )? <identifier>
__Sample:__
bc(sample). DROP KEYSPACE myApp;
A @DROP KEYSPACE@ statement results in the immediate, irreversible removal of an existing keyspace, including all column families in it, and all data contained in those column families.
If the keyspace does not exists, the statement will return an error, unless @IF EXISTS@ is used in which case the operation is a no-op.
h3(#createTableStmt). CREATE TABLE
__Syntax:__
bc(syntax)..
<create-table-stmt> ::= CREATE ( TABLE | COLUMNFAMILY ) ( IF NOT EXISTS )? <tablename>
'(' <definition> ( ',' <definition> )* ')'
( WITH <option> ( AND <option>)* )?
<column-definition> ::= <identifier> <type> ( PRIMARY KEY )?
| PRIMARY KEY '(' <partition-key> ( ',' <identifier> )* ')'
<partition-key> ::= <partition-key>
| '(' <partition-key> ( ',' <identifier> )* ')'
<partition-key> ::= <identifier>
| '(' <identifier> (',' <identifier> )* ')'
<option> ::= <property>
| COMPACT STORAGE
| CLUSTERING ORDER
p.
__Sample:__
bc(sample)..
CREATE TABLE monkeySpecies (
species text PRIMARY KEY,
common_name text,
population varint,
average_size int
) WITH comment='Important biological records'
AND read_repair_chance = 1.0;
CREATE TABLE timeline (
userid uuid,
posted_month int,
posted_time uuid,
body text,
posted_by text,
PRIMARY KEY (userid, posted_month, posted_time)
) WITH compaction = { 'class' : 'LeveledCompactionStrategy' };
p.
The @CREATE TABLE@ statement creates a new table. Each such table is a set of _rows_ (usually representing related entities) for which it defines a number of properties. A table is defined by a "name":#createTableName, it defines the <a href="#createTableColumn"><it>columns</it></a> composing rows of the table and have a number of "options":#createTableOptions. Note that the @CREATE COLUMNFAMILY@ syntax is supported as an alias for @CREATE TABLE@ (for historical reasons).
Attempting to create an already existing table will return an error unless the @IF NOT EXISTS@ option is used. If it is used, the statement will be a no-op if the table already exists.
h4(#createTableName). @<tablename>@
Valid table names are the same than valid "keyspace names":#createKeyspaceStmt (up to 32 characters long alphanumerical identifiers). If the table name is provided alone, the table is created within the current keyspace (see <a href="#useStmt"><tt>USE</tt></a>), but if it is prefixed by an existing keyspace name (see "@<tablename>@":#statements grammar), it is created in the specified keyspace (but does *not* change the current keyspace).
h4(#createTableColumn). @<column-definition>@
A @CREATE TABLE@ statement defines the columns that rows of the table can have. A _column_ is defined by its name (an identifier) and its type (see the "data types":#types section for more details on allowed types and their properties).
Within a table, a row is uniquely identified by its @PRIMARY KEY@ (or more simply the key), and hence all table definitions *must* define a PRIMARY KEY (and only one). A @PRIMARY KEY@ is composed of one or more of the columns defined in the table. If the @PRIMARY KEY@ is only one column, this can be specified directly after the column definition. Otherwise, it must be specified by following @PRIMARY KEY@ by the comma-separated list of column names composing the key within parenthesis. Note that:
bc(sample).
CREATE TABLE t (
k int PRIMARY KEY,
other text
)
is equivalent to
bc(sample).
CREATE TABLE t (
k int,
other text,
PRIMARY KEY (k)
)
Moreover, a table must define at least one column that is not part of the PRIMARY KEY as a row exists in Cassandra only if it contains at least one value for one such column.
h4(#createTablepartitionClustering). Partition key and clustering
In CQL, the order in which columns are defined for the @PRIMARY KEY@ matters. The first column of the key is called the __partition key__. It has the property that all the rows sharing the same partition key (even across table in fact) are stored on the same physical node. Also, insertion/update/deletion on rows sharing the same partition key for a given table are performed __atomically__ and in __isolation__. Note that it is possible to have a composite partition key, i.e. a partition key formed of multiple columns, using an extra set of parentheses to define which columns forms the partition key.
The remaining columns of the @PRIMARY KEY@ definition, if any, are called __clustering columns. On a given physical node, rows for a given partition key are stored in the order induced by the clustering columns, making the retrieval of rows in that clustering order particularly efficient (see <a href="#selectStmt"><tt>SELECT</tt></a>).
h4(#createTableOptions). @<option>@
The @CREATE TABLE@ statement supports a number of options that controls the configuration of a new table. These options can be specified after the @WITH@ keyword.
The first of these option is @COMPACT STORAGE@. This option is meanly targeted towards backward compatibility with some table definition created before CQL3. But it also provides a slightly more compact layout of data on disk, though at the price of flexibility and extensibility, and for that reason is not recommended unless for the backward compatibility reason. The restriction for table with @COMPACT STORAGE@ is that they support one and only one column outside of the ones part of the @PRIMARY KEY@. It also follows that columns cannot be added nor removed after creation. A table with @COMPACT STORAGE@ must also define at least one "clustering key":createTablepartitionClustering.
Another option is @CLUSTERING ORDER@. It allows to define the ordering of rows on disk. It takes the list of the clustering key names with, for each of them, the on-disk order (Ascending or descending). Note that this option affects "what @ORDER BY@ are allowed during @SELECT@":#selectOrderBy.
Table creation supports the following other @<property>@:
|_. option |_. kind |_. default |_. description|
|@comment@ | _simple_ | none | A free-form, human-readable comment.|
|@read_repair_chance@ | _simple_ | 0.1 | The probability with which to query extra nodes (e.g. more nodes than required by the consistency level) for the purpose of read repairs.|
|@dclocal_read_repair_chance@ | _simple_ | 0 | The probability with which to query extra nodes (e.g. more nodes than required by the consistency level) belonging to the same data center than the read coordinator for the purpose of read repairs.|
|@gc_grace_seconds@ | _simple_ | 864000 | Time to wait before garbage collecting tombstones (deletion markers).|
|@bloom_filter_fp_chance@ | _simple_ | 0.00075 | The target probability of false positive of the sstable bloom filters. Said bloom filters will be sized to provide the provided probability (thus lowering this value impact the size of bloom filters in-memory and on-disk)|
|@compaction@ | _map_ | _see below_ | The compaction options to use, see below.|
|@compression@ | _map_ | _see below_ | Compression options, see below. |
|@replicate_on_write@ | _simple_ | true | Whether to replicate data on write. This can only be set to false for tables with counters values. Disabling this is dangerous and can result in random lose of counters, don't disable unless you are sure to know what you are doing|
|@caching@ | _simple_ | keys_only | Whether to cache keys ("key cache") and/or rows ("row cache") for this table. Valid values are: @all@, @keys_only@, @rows_only@ and @none@. |
h4(#compactionOptions). @compaction@ options
The @compaction@ property must at least define the @'class'@ sub-option, that defines the compaction strategy class to use. The default supported class are @'SizeTieredCompactionStrategy'@ and @'LeveledCompactionStrategy'@. Custom strategy can be provided by specifying the full class name as a "string constant":#constants. The rest of the sub-options depends on the chosen class. The sub-options supported by the default classes are:
|_. option |_. supported compaction strategy |_. default |_. description |
| @tombstone_threshold@ | _all_ | 0.2 | A ratio such that if a sstable has more than this ratio of gcable tombstones over all contained columns, the sstable will be compacted (with no other sstables) for the purpose of purging those tombstones. |
| @tombstone_compaction_interval@ | _all_ | 1 day | The minimum time to wait after an sstable creation time before considering it for "tombstone compaction", where "tombstone compaction" is the compaction triggered if the sstable has more gcable tombstones than @tombstone_threshold@. |
| @min_sstable_size@ | SizeTieredCompactionStrategy | 50MB | The size tiered strategy groups SSTables to compact in buckets. A bucket groups SSTables that differs from less than 50% in size. However, for small sizes, this would result in a bucketing that is too fine grained. @min_sstable_size@ defines a size threshold (in bytes) below which all SSTables belong to one unique bucket|
| @min_threshold@ | SizeTieredCompactionStrategy | 4 | Minimum number of SSTables needed to start a minor compaction.|
| @max_threshold@ | SizeTieredCompactionStrategy | 32 | Maximum number of SSTables processed by one minor compaction.|
| @bucket_low@ | SizeTieredCompactionStrategy | 0.5 | Size tiered consider sstables to be within the same bucket if their size is within [average_size * @bucket_low@, average_size * @bucket_high@ ] (i.e the default groups sstable whose sizes diverges by at most 50%)|
| @bucket_high@ | SizeTieredCompactionStrategy | 1.5 | Size tiered consider sstables to be within the same bucket if their size is within [average_size * @bucket_low@, average_size * @bucket_high@ ] (i.e the default groups sstable whose sizes diverges by at most 50%).|
| @sstable_size_in_mb@ | LeveledCompactionStrategy | 5MB | The target size (in MB) for sstables in the leveled strategy. Note that while sstable sizes should stay less or equal to @sstable_size_in_mb@, it is possible to exceptionally have a larger sstable as during compaction, data for a given partition key are never split into 2 sstables|
For the @compression@ property, the following default sub-options are available:
|_. option |_. default |_. description |
| @sstable_compression@ | SnappyCompressor | The compression algorithm to use. Default compressor are: SnappyCompressor and DeflateCompressor. Use an empty string (@''@) to disable compression. Custom compressor can be provided by specifying the full class name as a "string constant":#constants.|
| @chunk_length_kb@ | 64KB | On disk SSTables are compressed by block (to allow random reads). This defines the size (in KB) of said block. Bigger values may improve the compression rate, but increases the minimum size of data to be read from disk for a read |
| @crc_check_chance@ | 1.0 | When compression is enabled, each compressed block includes a checksum of that block for the purpose of detecting disk bitrot and avoiding the propagation of corruption to other replica. This option defines the probability with which those checksums are checked during read. By default they are always checked. Set to 0 to disable checksum checking and to 0.5 for instance to check them every other read|
h4. Other considerations:
* When "inserting":#insertStmt/"updating":#updateStmt a given row, not all columns needs to be defined (except for those part of the key), and missing columns occupy no space on disk. Furthermore, adding new columns (see <a href=#alterStmt><tt>ALTER TABLE</tt></a>) is a constant time operation. There is thus no need to try to anticipate future usage (or to cry when you haven't) when creating a table.
h3(#alterTableStmt). ALTER TABLE
__Syntax:__
bc(syntax)..
<alter-table-stmt> ::= ALTER (TABLE | COLUMNFAMILY) <tablename> <instruction>
<instruction> ::= ALTER <identifier> TYPE <type>
| ADD <identifier> <type>
| DROP <identifier>
| WITH <option> ( AND <option> )*
p.
__Sample:__
bc(sample)..
ALTER TABLE addamsFamily
ALTER lastKnownLocation TYPE uuid;
ALTER TABLE addamsFamily
ADD gravesite varchar;
ALTER TABLE addamsFamily
WITH comment = 'A most excellent and useful column family'
AND read_repair_chance = 0.2;
p.
The @ALTER@ statement is used to manipulate table definitions. It allows to add new columns, drop existing ones, change the type of existing columns, or update the table options. As for table creation, @ALTER COLUMNFAMILY@ is allowed as an alias for @ALTER TABLE@.
The @<tablename>@ is the table name optionally preceded by the keyspace name. The @<instruction>@ defines the alteration to perform:
* @ALTER@: Update the type of a given defined column. Note that the type of the "clustering columns":#createTablepartitionClustering cannot be modified as it induces the on-disk ordering of rows. Columns on which a "secondary index":#createIndexStmt is defined have the same restriction. Other columns are free from those restrictions (no validation of existing data is performed), but it is usually a bad idea to change the type to a non-compatible one, unless no data have been inserted for that column yet, as this could confuse CQL drivers/tools.
* @ADD@: Adds a new column to the table. The @<identifier>@ for the new column must not conflict with an existing column. Moreover, columns cannot be added to tables defined with the @COMPACT STORAGE@ option.
* @DROP@: Removes a column from the table. Dropped columns will immediately become unavailable in the queries and will not be included in compacted sstables in the future. If a column is readded, queries won't return values written before the column was last dropped. It is assumed that timestamps represent actual time, so if this is not your case, you should NOT readd previously dropped columns. Columns can't be dropped from tables defined with the @COMPACT STORAGE@ option.
* @WITH@: Allows to update the options of the table. The "supported @<option>@":#createTableOptions (and syntax) are the same as for the @CREATE TABLE@ statement except that @COMPACT STORAGE@ is not supported. Note that setting any @compaction@ sub-options has the effect of erasing all previous @compaction@ options, so you need to re-specify all the sub-options if you want to keep them. The same note applies to the set of @compression@ sub-options.
h3(#dropTableStmt). DROP TABLE
__Syntax:__
bc(syntax). <drop-table-stmt> ::= DROP TABLE ( IF EXISTS )? <tablename>
__Sample:__
bc(sample). DROP TABLE worldSeriesAttendees;
The @DROP TABLE@ statement results in the immediate, irreversible removal of a table, including all data contained in it. As for table creation, @DROP COLUMNFAMILY@ is allowed as an alias for @DROP TABLE@.
If the table does not exists, the statement will return an error, unless @IF EXISTS@ is used in which case the operation is a no-op.
h3(#truncateStmt). TRUNCATE
__Syntax:__
bc(syntax). <truncate-stmt> ::= TRUNCATE <tablename>
__Sample:__
bc(sample). TRUNCATE superImportantData;
The @TRUNCATE@ statement permanently removes all data from a table.
h3(#createIndexStmt). CREATE INDEX
__Syntax:__
bc(syntax). <create-index-stmt> ::= CREATE ( CUSTOM )? INDEX ( IF NOT EXISTS )? <identifier>? ON <tablename> '(' <identifier> ')'
( USING <string> ( WITH OPTIONS = <map-literal> )? )?
__Sample:__
bc(sample).
CREATE INDEX userIndex ON NerdMovies (user);
CREATE INDEX ON Mutants (abilityId);
CREATE CUSTOM INDEX ON users (email) USING 'path.to.the.IndexClass';
CREATE CUSTOM INDEX ON users (email) USING 'path.to.the.IndexClass' WITH OPTIONS = {'storage': '/mnt/ssd/indexes/'};
The @CREATE INDEX@ statement is used to create a new (automatic) secondary index for a given (existing) column in a given table. A name for the index itself can be specified before the @ON@ keyword, if desired. If data already exists for the column, it will be indexed asynchronously. After the index is created, new data for the column is indexed automatically at insertion time.
Attempting to create an already existing index will return an error unless the @IF NOT EXISTS@ option is used. If it is used, the statement will be a no-op if the index already exists.
h3(#dropIndexStmt). DROP INDEX
__Syntax:__
bc(syntax). <drop-index-stmt> ::= DROP INDEX ( IF EXISTS )? <identifier>
__Sample:__
bc(sample). DROP INDEX userIndex;
The @DROP INDEX@ statement is used to drop an existing secondary index. The argument of the statement is the index name.
If the index does not exists, the statement will return an error, unless @IF EXISTS@ is used in which case the operation is a no-op.
h2(#dataManipulation). Data Manipulation
h3(#insertStmt). INSERT
__Syntax:__
bc(syntax)..
<insertStatement> ::= INSERT INTO <tablename>
'(' <identifier> ( ',' <identifier> )* ')'
VALUES '(' <term-or-literal> ( ',' <term-or-literal> )* ')'
( IF NOT EXISTS )?
( USING <option> ( AND <option> )* )?
<term-or-literal> ::= <term>
| <collection-literal>
<option> ::= TIMESTAMP <integer>
| TTL <integer>
p.
__Sample:__
bc(sample).
INSERT INTO NerdMovies (movie, director, main_actor, year)
VALUES ('Serenity', 'Joss Whedon', 'Nathan Fillion', 2005)
USING TTL 86400;
The @INSERT@ statement writes one or more columns for a given row in a table. Note that since a row is identified by its @PRIMARY KEY@, the columns that compose it must be specified. Also, since a row only exists when it contains one value for a column not part of the @PRIMARY KEY@, one such value must be specified too.
Note that unlike in SQL, @INSERT@ does not check the prior existence of the row by default: the row is created if none existed before, and updated otherwise. Furthermore, there is no mean to know which of creation or update happened.
It is however possible to use the @IF NOT EXISTS@ condition to only insert if the row does not exist prior to the insertion. But please note that using @IF NOT EXISTS@ will incur a non negligible performance cost (internally, Paxos will be used) so this should be used sparingly.
All updates for an @INSERT@ are applied atomically and in isolation.
Please refer to the "@UPDATE@":#updateOptions section for information on the @<option>@ available and to the "collections":#collections section for use of @<collection-literal>@. Also note that @INSERT@ does not support counters, while @UPDATE@ does.
h3(#updateStmt). UPDATE
__Syntax:__
bc(syntax)..
<update-stmt> ::= UPDATE <tablename>
( USING <option> ( AND <option> )* )?
SET <assignment> ( ',' <assignment> )*
WHERE <where-clause>
( IF <identifier> '=' <term> ( AND <identifier> '=' <term> )* )?
<assignment> ::= <identifier> '=' <term>
| <identifier> '=' <identifier> ('+' | '-') (<int-term> | <set-literal> | <list-literal>)
| <identifier> '=' <identifier> '+' <map-literal>
| <identifier> '[' <term> ']' '=' <term>
<where-clause> ::= <relation> ( AND <relation> )*
<relation> ::= <identifier> '=' <term>
| <identifier> IN '(' ( <term> ( ',' <term> )* )? ')'
| <identifier> IN '?'
<option> ::= TIMESTAMP <integer>
| TTL <integer>
p.
__Sample:__
bc(sample)..
UPDATE NerdMovies USING TTL 400
SET director = 'Joss Whedon',
main_actor = 'Nathan Fillion',
year = 2005
WHERE movie = 'Serenity';
UPDATE UserActions SET total = total + 2 WHERE user = B70DE1D0-9908-4AE3-BE34-5573E5B09F14 AND action = 'click';
p.
The @UPDATE@ statement writes one or more columns for a given row in a table. The @<where-clause>@ is used to select the row to update and must include all columns composing the @PRIMARY KEY@ (the @IN@ relation is only supported for the last column of the partition key). Other columns values are specified through @<assignment>@ after the @SET@ keyword.
Note that unlike in SQL, @UPDATE@ does not check the prior existence of the row by default: the row is created if none existed before, and updated otherwise. Furthermore, there is no mean to know which of creation or update happened.
It is however possible to use the conditions on some columns through @IF@, in which case the row will not be updated unless such condition are met. But please note that using @IF@ conditions will incur a non negligible performance cost (internally, Paxos will be used) so this should be used sparingly.
In an @UPDATE@ statement, all updates within the same partition key are applied atomically and in isolation.
The @c = c + 3@ form of @<assignment>@ is used to increment/decrement counters. The identifier after the '=' sign *must* be the same than the one before the '=' sign (Only increment/decrement is supported on counters, not the assignment of a specific value).
The @id = id + <collection-literal>@ and @id[value1] = value2@ forms of @<assignment>@ are for collections. Please refer to the "relevant section":#collections for more details.
h4(#updateOptions). @<options>@
The @UPDATE@ and @INSERT@ statements allows to specify the following options for the insertion:
* @TIMESTAMP@: sets the timestamp for the operation. If not specified, the current time of the insertion (in microseconds) is used. This is usually a suitable default.
* @TTL@: allows to specify an optional Time To Live (in seconds) for the inserted values. If set, the inserted values are automatically removed from the database after the specified time. Note that the TTL concerns the inserted values, not the column themselves. This means that any subsequent update of the column will also reset the TTL (to whatever TTL is specified in that update). By default, values never expire.
h3(#deleteStmt). DELETE
__Syntax:__
bc(syntax)..
<delete-stmt> ::= DELETE ( <selection> ( ',' <selection> )* )?
FROM <tablename>
( USING TIMESTAMP <integer>)?
WHERE <where-clause>
<selection> ::= <identifier> ( '[' <term> ']' )?
<where-clause> ::= <relation> ( AND <relation> )*
<relation> ::= <identifier> '=' <term>
| <identifier> IN '(' ( <term> ( ',' <term> )* )? ')'
| <identifier> IN '?'
p.
__Sample:__
bc(sample)..
DELETE FROM NerdMovies USING TIMESTAMP 1240003134 WHERE movie = 'Serenity';
DELETE phone FROM Users WHERE userid IN (C73DE1D3-AF08-40F3-B124-3FF3E5109F22, B70DE1D0-9908-4AE3-BE34-5573E5B09F14);
p.
The @DELETE@ statement deletes columns and rows. If column names are provided directly after the @DELETE@ keyword, only those columns are deleted from the row indicated by the @<where-clause>@ (the @id[value]@ syntax in @<selection>@ is for collection, please refer to the "collection section":#collections for more details). Otherwise whole rows are removed. The @<where-clause>@ allows to specify the key for the row(s) to delete (the @IN@ relation is only supported for the last column of the partition key).
@DELETE@ supports the @TIMESTAMP@ options with the same semantic that in the "@UPDATE@":#updateStmt statement.
In a @DELETE@ statement, all deletions within the same partition key are applied atomically and in isolation.
h3(#batchStmt). BATCH
__Syntax:__
bc(syntax)..
<batch-stmt> ::= BEGIN BATCH
( USING <option> ( AND <option> )* )?
<modification-stmt> ( ';' <modification-stmt> )*
APPLY BATCH
<modification-stmt> ::= <insert-stmt>
| <update-stmt>
| <delete-stmt>
<option> ::= TIMESTAMP <integer>
p.
__Sample:__
bc(sample).
BEGIN BATCH
INSERT INTO users (userid, password, name) VALUES ('user2', 'ch@ngem3b', 'second user');
UPDATE users SET password = 'ps22dhds' WHERE userid = 'user3';
INSERT INTO users (userid, password) VALUES ('user4', 'ch@ngem3c');
DELETE name FROM users WHERE userid = 'user1';
APPLY BATCH;
The @BATCH@ statement group multiple modification statements (insertions/updates and deletions) into a single statement. It mainly serves two purposes:
# it saves network round-trips between the client and the server (and sometimes between the server coordinator and the replicas) when batching multiple updates.
# all updates in a @BATCH@ belonging to a given partition key are performed atomically and in isolation
Note however that the @BATCH@ statement only allows @UPDATE@, @INSERT@ and @DELETE@ statements and is _not_ a full analogue for SQL transactions.
h4(#batchOptions). @<option>@
@BATCH@ supports both the @TIMESTAMP@ option, with similar semantic to the one described in the "@UPDATE@":#updateOptions statement (the timestamp applies to all the statement inside the batch). However, if used, @TIMESTAMP@ *must not* be used in the statements within the batch.
h2(#queries). Queries
h3(#selectStmt). SELECT
__Syntax:__
bc(syntax)..
<select-stmt> ::= SELECT <select-clause>
FROM <tablename>
( WHERE <where-clause> )?
( ORDER BY <order-by> )?
( LIMIT <integer> )?
( ALLOW FILTERING )?
<select-clause> ::= DISTINCT? <selection-list>
| COUNT '(' ( '*' | '1' ) ')' (AS <identifier>)?
<selection-list> ::= <selector> (AS <identifier>)? ( ',' <selector> (AS <identifier>)? )*
| '*'
<selector> ::= <identifier>
| WRITETIME '(' <identifier> ')'
| TTL '(' <identifier> ')'
| <function> '(' (<selector> (',' <selector>)*)? ')'
<where-clause> ::= <relation> ( AND <relation> )*
<relation> ::= <identifier> ('=' | '<' | '>' | '<=' | '>=') <term>
| <identifier> IN '(' ( <term> ( ',' <term>)* )? ')'
| TOKEN '(' <identifier> ( ',' <identifer>)* ')' ('=' | '<' | '>' | '<=' | '>=') <term>
<order-by> ::= <ordering> ( ',' <odering> )*
<ordering> ::= <identifer> ( ASC | DESC )?
p.
__Sample:__
bc(sample)..
SELECT name, occupation FROM users WHERE userid IN (199, 200, 207);
SELECT name AS user_name, occupation AS user_occupation FROM users;
SELECT time, value
FROM events
WHERE event_type = 'myEvent'
AND time > '2011-02-03'
AND time <= '2012-01-01'
SELECT COUNT(*) FROM users;
SELECT COUNT(*) AS user_count FROM users;
p.
The @SELECT@ statements reads one or more columns for one or more rows in a table. It returns a result-set of rows, where each row contains the collection of columns corresponding to the query.
h4(#selectSelection). @<select-clause>@
The @<select-clause>@ determines which columns needs to be queried and returned in the result-set. It consists of either the comma-separated list of <selector> or the wildcard character (@*@) to select all the columns defined for the table.
A @<selector>@ is either a column name to retrieve, or a @<function>@ of one or multiple column names. The functions allows are the same that for @<term>@ and are describe in the "function section":#function. In addition to these generic functions, the @WRITETIME@ (resp. @TTL@) function allows to select the timestamp of when the column was inserted (resp. the time to live (in seconds) for the column (or null if the column has no expiration set)).
Any @<selector>@ can be aliased using @AS@ keyword (see examples). Please note that @<where-clause>@ and @<order-by>@ clause should refer to the columns by their original names and not by their aliases.
The @COUNT@ keyword can be used with parenthesis enclosing @*@. If so, the query will return a single result: the number of rows matching the query. Note that @COUNT(1)@ is supported as an alias.
h4(#selectWhere). @<where-clause>@
The @<where-clause>@ specifies which rows must be queried. It is composed of relations on the columns that are part of the @PRIMARY KEY@ and/or have a "secondary index":#createIndexStmt defined on them.
Not all relations are allowed in a query. For instance, non-equal relations (where @IN@ is considered as an equal relation) on a partition key are not supported (but see the use of the @TOKEN@ method below to do non-equal queries on the partition key). Moreover, for a given partition key, the clustering columns induce an ordering of rows and relations on them is restricted to the relations that allow to select a *contiguous* (for the ordering) set of rows. For instance, given
bc(sample).
CREATE TABLE posts (
userid text,
blog_title text,
posted_at timestamp,
entry_title text,
content text,
category int,
PRIMARY KEY (userid, blog_title, posted_at)
)
The following query is allowed:
bc(sample).
SELECT entry_title, content FROM posts WHERE userid='john doe' AND blog_title='John's Blog' AND posted_at >= '2012-01-01' AND posted_at < '2012-01-31'
But the following one is not, as it does not select a contiguous set of rows (and we suppose no secondary indexes are set):
bc(sample).
// Needs a blog_title to be set to select ranges of posted_at
SELECT entry_title, content FROM posts WHERE userid='john doe' AND posted_at >= '2012-01-01' AND posted_at < '2012-01-31'
When specifying relations, the @TOKEN@ function can be used on the @PARTITION KEY@ column to query. In that case, rows will be selected based on the token of their @PARTITION_KEY@ rather than on the value. Note that the token of a key depends on the partitioner in use, and that in particular the RandomPartitioner won't yield a meaningful order. Also note that ordering partitioners always order token values by bytes (so even if the partition key is of type int, @token(-1) > token(0)@ in particular). Example:
bc(sample).
SELECT * FROM posts WHERE token(userid) > token('tom') AND token(userid) < token('bob')
Moreover, the @IN@ relation is only allowed on the last column of the partition key and on the last column of the full primary key.
h4(#selectOrderBy). @<order-by>@
The @ORDER BY@ option allows to select the order of the returned results. It takes as argument a list of column names along with the order for the column (@ASC@ for ascendant and @DESC@ for descendant, omitting the order being equivalent to @ASC@). Currently the possible orderings are limited (which depends on the table "@CLUSTERING ORDER@":#createTableOptions):
* if the table has been defined without any specific @CLUSTERING ORDER@, then then allowed orderings are the order induced by the clustering key and the reverse of that one.
* otherwise, the orderings allowed are the order of the @CLUSTERING ORDER@ option and the reversed one.
h4(#selectLimit). @LIMIT@
The @LIMIT@ option to a @SELECT@ statement limits the number of rows returned by a query.
h4(#selectAllowFiltering). @ALLOW FILTERING@
By default, CQL only allows select queries that don't involve "filtering" server side, i.e. queries where we know that all (live) record read will be returned (maybe partly) in the result set. The reasoning is that those "non filtering" queries have predictable performance in the sense that they will execute in a time that is proportional to the amount of data *returned* by the query (which can be controlled through @LIMIT@).
The @ALLOW FILTERING@ option allows to explicitly allow (some) queries that require filtering. Please note that a query using @ALLOW FILTERING@ may thus have unpredictable performance (for the definition above), i.e. even a query that selects a handful of records *may* exhibit performance that depends on the total amount of data stored in the cluster.
For instance, considering the following table holding user profiles with their year of birth (with a secondary index on it) and country of residence:
bc(sample)..
CREATE TABLE users (
username text PRIMARY KEY,
firstname text,
lastname text,
birth_year int,
country text
)
CREATE INDEX ON users(birth_year);
p.
Then the following queries are valid:
bc(sample).
SELECT * FROM users;
SELECT firstname, lastname FROM users WHERE birth_year = 1981;
because in both case, Cassandra guarantees that these queries performance will be proportional to the amount of data returned. In particular, if no users are born in 1981, then the second query performance will not depend of the number of user profile stored in the database (not directly at least: due to secondary index implementation consideration, this query may still depend on the number of node in the cluster, which indirectly depends on the amount of data stored. Nevertheless, the number of nodes will always be multiple number of magnitude lower than the number of user profile stored). Of course, both query may return very large result set in practice, but the amount of data returned can always be controlled by adding a @LIMIT@.
However, the following query will be rejected:
bc(sample).
SELECT firstname, lastname FROM users WHERE birth_year = 1981 AND country = 'FR';
because Cassandra cannot guarantee that it won't have to scan large amount of data even if the result to those query is small. Typically, it will scan all the index entries for users born in 1981 even if only a handful are actually from France. However, if you "know what you are doing", you can force the execution of this query by using @ALLOW FILTERING@ and so the following query is valid:
bc(sample).
SELECT firstname, lastname FROM users WHERE birth_year = 1981 AND country = 'FR' ALLOW FILTERING;
h2(#types). Data Types
CQL supports a rich set of data types for columns defined in a table, including collection types. On top of those native and collection types, users can also provide custom types (through a JAVA class extending @AbstractType@ loadable by Cassandra). The syntax of types is thus:
bc(syntax)..
<type> ::= <native-type>
| <collection-type>
| <string> // Used for custom types. The fully-qualified name of a JAVA class
<native-type> ::= ascii
| bigint
| blob
| boolean
| counter
| decimal
| double
| float
| inet
| int
| text
| timestamp
| timeuuid
| uuid
| varchar
| varint
<collection-type> ::= list '<' <native-type> '>'
| set '<' <native-type> '>'
| map '<' <native-type> ',' <native-type> '>'
p. Note that the native types are keywords and as such are case-insensitive. They are however not reserved ones.
p. The following table gives additional informations on the native data types, and on which kind of "constants":#constants each type supports:
|_. type |_. constants supported|_. description|
|@ascii@ | strings |ASCII character string|
|@bigint@ | integers |64-bit signed long|
|@blob@ | blobs |Arbitrary bytes (no validation)|
|@boolean@ | booleans |true or false|
|@counter@ | integers |Counter column (64-bit signed value). See "Counters":#counters for details|
|@decimal@ | integers, floats |Variable-precision decimal|
|@double@ | integers |64-bit IEEE-754 floating point|
|@float@ | integers, floats |32-bit IEEE-754 floating point|
|@inet@ | strings |An IP address. It can be either 4 bytes long (IPv4) or 16 bytes long (IPv6). There is no @inet@ constant, IP address should be inputed as strings|
|@int@ | integers |32-bit signed int|
|@text@ | strings |UTF8 encoded string|
|@timestamp@| integers, strings |A timestamp. Strings constant are allow to input timestamps as dates, see "Working with dates":#usingdates below for more information.|
|@timeuuid@ | uuids |Type 1 UUID. This is generally used as a "conflict-free" timestamp. Also see the "functions on Timeuuid":#timeuuidFun|
|@uuid@ | uuids |Type 1 or type 4 UUID|
|@varchar@ | strings |UTF8 encoded string|
|@varint@ | integers |Arbitrary-precision integer|
For more information on how to use the collection types, see the "Working with collections":#collections section below.
h3(#usingdates). Working with dates
Values of the @timestamp@ type are encoded as 64-bit signed integers representing a number of milliseconds since the standard base time known as "the epoch": January 1 1970 at 00:00:00 GMT.
Timestamp can be input in CQL as simple long integers, giving the number of milliseconds since the epoch, as defined above.
They can also be input as string literals in any of the following ISO 8601 formats, each representing the time and date Mar 2, 2011, at 04:05:00 AM, GMT.:
* @2011-02-03 04:05+0000@
* @2011-02-03 04:05:00+0000@
* @2011-02-03 04:05:00.000+0000@
* @2011-02-03T04:05+0000@
* @2011-02-03T04:05:00+0000@
* @2011-02-03T04:05:00.000+0000@
The @+0000@ above is an RFC 822 4-digit time zone specification; @+0000@ refers to GMT. US Pacific Standard Time is @-0800@. The time zone may be omitted if desired-- the date will be interpreted as being in the time zone under which the coordinating Cassandra node is configured.
* @2011-02-03 04:05@
* @2011-02-03 04:05:00@
* @2011-02-03 04:05:00.000@
* @2011-02-03T04:05@
* @2011-02-03T04:05:00@
* @2011-02-03T04:05:00.000@
There are clear difficulties inherent in relying on the time zone configuration being as expected, though, so it is recommended that the time zone always be specified for timestamps when feasible.
The time of day may also be omitted, if the date is the only piece that matters:
* @2011-02-03@
* @2011-02-03+0000@
In that case, the time of day will default to 00:00:00, in the specified or default time zone.
h3(#counters). Counters
The @counter@ type is used to define _counter columns_. A counter column is a column whose value is a 64-bit signed integer and on which 2 operations are supported: incrementation and decrementation (see "@UPDATE@":#updateStmt for syntax). Note the value of a counter cannot be set. A counter doesn't exist until first incremented/decremented, and the first incrementation/decrementation is made as if the previous value was 0. Deletion of counter columns is supported but have some limitations (see the "Cassandra Wiki":http://wiki.apache.org/cassandra/Counters for more information).
The use of the counter type is limited in the following way:
* It cannot be used for column that is part of the @PRIMARY KEY@ of a table.
* A table that contains a counter can only contain counters. In other words, either all the columns of a table outside the @PRIMARY KEY@ have the counter type, or none of them have it.
h3(#collections). Working with collections
h4. Noteworthy characteristics
Collections are meant for storing/denormalizing relatively small amount of data. They work well for things like "the phone numbers of a given user", "labels applied to an email", etc. But when items are expected to grow unbounded ("all the messages sent by a given user", "events registered by a sensor", ...), then collections are not appropriate anymore and a specific table (with clustering columns) should be used. Concretely, collections have the following limitations:
* Collections are always read in their entirety (and reading one is not paged internally).
* Collections cannot have more than 65535 elements. More precisely, while it may be possible to insert more than 65535 elements, it is not possible to read more than the 65535 first elements (see "CASSANDRA-5428":https://issues.apache.org/jira/browse/CASSANDRA-5428 for details).
* While insertion operations on sets and maps never incur a read-before-write internally, some operations on lists do (see the section on lists below for details). It is thus advised to prefer sets over lists when possible.
Please note that while some of those limitations may or may not be loosen in the future, the general rule that collections are for denormalizing small amount of data is meant to stay.
h4(#map). Maps
A @map@ is a "typed":#types set of key-value pairs, where keys are unique. Furthermore, note that the map are internally sorted by their keys and will thus always be returned in that order. To create a column of type @map@, use the @map@ keyword suffixed with comma-separated key and value types, enclosed in angle brackets. For example:
bc(sample).
CREATE TABLE users (
id text PRIMARY KEY,
given text,
surname text,
favs map<text, text> // A map of text keys, and text values
)
Writing @map@ data is accomplished with a JSON-inspired syntax. To write a record using @INSERT@, specify the entire map as a JSON-style associative array. _Note: This form will always replace the entire map._
bc(sample).
// Inserting (or Updating)
INSERT INTO users (id, given, surname, favs)
VALUES ('jsmith', 'John', 'Smith', { 'fruit' : 'apple', 'band' : 'Beatles' })
Adding or updating key-values of a (potentially) existing map can be accomplished either by subscripting the map column in an @UPDATE@ statement or by adding a new map literal:
bc(sample).
// Updating (or inserting)
UPDATE users SET favs['author'] = 'Ed Poe' WHERE id = 'jsmith'
UPDATE users SET favs = favs + { 'movie' : 'Cassablanca' } WHERE id = 'jsmith'
Note that TTLs are allowed for both @INSERT@ and @UPDATE@, but in both case the TTL set only apply to the newly inserted/updated _values_. In other words,
bc(sample).
// Updating (or inserting)
UPDATE users USING TTL 10 SET favs['color'] = 'green' WHERE id = 'jsmith'
will only apply the TTL to the @{ 'color' : 'green' }@ record, the rest of the map remaining unaffected.
Deleting a map record is done with:
bc(sample).
DELETE favs['author'] FROM users WHERE id = 'jsmith'
h4(#set). Sets
A @set@ is a "typed":#types collection of unique values. Sets are ordered by their values. To create a column of type @set@, use the @set@ keyword suffixed with the value type enclosed in angle brackets. For example:
bc(sample).
CREATE TABLE images (
name text PRIMARY KEY,
owner text,
date timestamp,
tags set<text>
);
Writing a @set@ is accomplished by comma separating the set values, and enclosing them in curly braces. _Note: An @INSERT@ will always replace the entire set._
bc(sample).
INSERT INTO images (name, owner, date, tags)
VALUES ('cat.jpg', 'jsmith', 'now', { 'kitten', 'cat', 'pet' });
Adding and removing values of a set can be accomplished with an @UPDATE@ by adding/removing new set values to an existing @set@ column.
bc(sample).
UPDATE images SET tags = tags + { 'cute', 'cuddly' } WHERE name = 'cat.jpg';
UPDATE images SET tags = tags - { 'lame' } WHERE name = 'cat.jpg';
As with "maps":#map, TTLs if used only apply to the newly inserted/updated _values_.
h4(#list). Lists
A @list@ is a "typed":#types collection of non-unique values where elements are ordered by there position in the list. To create a column of type @list@, use the @list@ keyword suffixed with the value type enclosed in angle brackets. For example:
bc(sample).
CREATE TABLE plays (
id text PRIMARY KEY,
game text,
players int,
scores list<int>
)
Do note that as explained below, lists have some limitations and performance considerations to take into account, and it is advised to prefer "sets":#set over lists when this is possible.
Writing @list@ data is accomplished with a JSON-style syntax. To write a record using @INSERT@, specify the entire list as a JSON array. _Note: An @INSERT@ will always replace the entire list._
bc(sample).
INSERT INTO plays (id, game, players, scores)
VALUES ('123-afde', 'quake', 3, [17, 4, 2]);
Adding (appending or prepending) values to a list can be accomplished by adding a new JSON-style array to an existing @list@ column.
bc(sample).
UPDATE plays SET players = 5, scores = scores + [ 14, 21 ] WHERE id = '123-afde';
UPDATE plays SET players = 5, scores = [ 12 ] + scores WHERE id = '123-afde';
It should be noted that append and prepend are not idempotent operations. This means that if during an append or a prepend the operation timeout, it is not always safe to retry the operation (as this could result in the record appended or prepended twice).
Lists also provides the following operation: setting an element by its position in the list, removing an element by its position in the list and remove all the occurrence of a given value in the list. _However, and contrarily to all the other collection operations, these three operations induce an internal read before the update, and will thus typically have slower performance characteristics_. Those operations have the following syntax:
bc(sample).
UPDATE plays SET scores[1] = 7 WHERE id = '123-afde'; // sets the 2nd element of scores to 7 (raises an error is scores has less than 2 elements)
DELETE scores[1] FROM plays WHERE id = '123-afde'; // deletes the 2nd element of scores (raises an error is scores has less than 2 elements)
UPDATE plays SET scores = scores - [ 12, 21 ] WHERE id = '123-afde'; // removes all occurrences of 12 and 21 from scores
As with "maps":#map, TTLs if used only apply to the newly inserted/updated _values_.
h2(#functions). Functions
CQL3 supports a few functions (more to come). Currently, it only support functions on values (functions that transform one or more column values into a new value) and in particular aggregation functions are not supported. The functions supported are described below:
h3(#tokenFun). Token
The @token@ function allows to compute the token for a given partition key. The exact signature of the token function depends on the table concerned and of the partitioner used by the cluster.
The type of the arguments of the @token@ depend on the type of the partition key columns. The return type depend on the partitioner in use:
* For Murmur3Partitioner, the return type is @bigint@.
* For RandomPartitioner, the return type is @varint@.
* For ByteOrderedPartitioner, the return type is @blob@.
For instance, in a cluster using the default Murmur3Partitioner, if a table is defined by
bc(sample).
CREATE TABLE users (
userid text PRIMARY KEY,
username text,
...
)
then the @token@ function will take a single argument of type @text@ (in that case, the partition key is @userid@ (there is no clustering key so the partition key is the same than the primary key)), and the return type will be @bigint@.
h3(#timeuuidFun). Timeuuid functions
h4. @now@
The @now@ function takes no arguments and generates a new unique timeuuid (at the time where the statement using it is executed). Note that this method is useful for insertion but is largely non-sensical in @WHERE@ clauses. For instance, a query of the form
bc(sample).
SELECT * FROM myTable WHERE t = now()
will never return any result by design, since the value returned by @now()@ is guaranteed to be unique.
h4. @minTimeuuid@ and @maxTimeuuid@
The @minTimeuuid@ (resp. @maxTimeuuid@) function takes a @timestamp@ value @t@ (which can be "either a timestamp or a date string":#usingdates) and return a _fake_ @timeuuid@ corresponding to the _smallest_ (resp. _biggest_) possible @timeuuid@ having for timestamp @t@. So for instance:
bc(sample).
SELECT * FROM myTable WHERE t > maxTimeuuid('2013-01-01 00:05+0000') AND t < minTimeuuid('2013-02-02 10:00+0000')
will select all rows where the @timeuuid@ column @t@ is strictly older than '2013-01-01 00:05+0000' but strictly younger than '2013-02-02 10:00+0000'. Please note that @t >= maxTimeuuid('2013-01-01 00:05+0000')@ would still _not_ select a @timeuuid@ generated exactly at '2013-01-01 00:05+0000' and is essentially equivalent to @t > maxTimeuuid('2013-01-01 00:05+0000')@.
_Warning_: We called the values generated by @minTimeuuid@ and @maxTimeuuid@ _fake_ UUID because they do no respect the Time-Based UUID generation process specified by the "RFC 4122":http://www.ietf.org/rfc/rfc4122.txt. In particular, the value returned by these 2 methods will not be unique. This means you should only use those methods for querying (as in the example above). Inserting the result of those methods is almost certainly _a bad idea_.
h4. @dateOf@ and @unixTimestampOf@
The @dateOf@ and @unixTimestampOf@ functions take a @timeuuid@ argument and extract the embedded timestamp. However, while the @dateof@ function return it with the @timestamp@ type (that most client, including cqlsh, interpret as a date), the @unixTimestampOf@ function returns it as a @bigint@ raw value.
h3(#blobFun). Blob conversion functions
A number of functions are provided to "convert" the native types into binary data (@blob@). For every @<native-type>@ @type@ supported by CQL3 (a notable exceptions is @blob@, for obvious reasons), the function @typeAsBlob@ takes a argument of type @type@ and return it as a @blob@. Conversely, the function @blobAsType@ takes a 64-bit @blob@ argument and convert it to a @bigint@ value. And so for instance, @bigintAsBlob(3)@ is @0x0000000000000003@ and @blobAsBigint(0x0000000000000003)@ is @3@.
h2(#appendixA). Appendix A: CQL Keywords
CQL distinguishes between _reserved_ and _non-reserved_ keywords. Reserved keywords cannot be used as identifier, they are truly reserved for the language (but one can enclose a reserved keyword by double-quotes to use it as an identifier). Non-reserved keywords however only have a specific meaning in certain context but can used as identifer otherwise. The only _raison d'être_ of these non-reserved keywords is convenience: some keyword are non-reserved when it was always easy for the parser to decide whether they were used as keywords or not.
|_. Keyword |_. Reserved? |
| @ADD@ | yes |
| @ALL@ | no |
| @ALTER@ | yes |
| @AND@ | yes |
| @ANY@ | yes |
| @APPLY@ | yes |
| @AS@ | no |
| @ASC@ | yes |
| @ASCII@ | no |
| @AUTHORIZE@ | yes |
| @BATCH@ | yes |
| @BEGIN@ | yes |
| @BIGINT@ | no |
| @BLOB@ | no |
| @BOOLEAN@ | no |
| @BY@ | yes |
| @CLUSTERING@ | no |
| @COLUMNFAMILY@ | yes |
| @COMPACT@ | no |
| @CONSISTENCY@ | no |
| @COUNT@ | no |
| @COUNTER@ | no |
| @CREATE@ | yes |
| @DECIMAL@ | no |
| @DELETE@ | yes |
| @DESC@ | yes |
| @DOUBLE@ | no |
| @DROP@ | yes |
| @EACH_QUORUM@ | yes |
| @FLOAT@ | no |
| @FROM@ | yes |
| @GRANT@ | yes |
| @IN@ | yes |
| @INDEX@ | yes |
| @CUSTOM@ | no |
| @INSERT@ | yes |
| @INT@ | no |
| @INTO@ | yes |
| @KEY@ | no |
| @KEYSPACE@ | yes |
| @LEVEL@ | no |
| @LIMIT@ | yes |
| @LOCAL_ONE@ | yes |
| @LOCAL_QUORUM@ | yes |
| @MODIFY@ | yes |
| @NORECURSIVE@ | yes |
| @NOSUPERUSER@ | no |
| @OF@ | yes |
| @ON@ | yes |
| @ONE@ | yes |
| @ORDER@ | yes |
| @PASSWORD@ | no |
| @PERMISSION@ | no |
| @PERMISSIONS@ | no |
| @PRIMARY@ | yes |
| @QUORUM@ | yes |
| @REVOKE@ | yes |
| @SCHEMA@ | yes |
| @SELECT@ | yes |
| @SET@ | yes |
| @STORAGE@ | no |
| @SUPERUSER@ | no |
| @TABLE@ | yes |
| @TEXT@ | no |
| @TIMESTAMP@ | no |
| @TIMEUUID@ | no |
| @THREE@ | yes |
| @TOKEN@ | yes |
| @TRUNCATE@ | yes |
| @TTL@ | no |
| @TWO@ | yes |
| @TYPE@ | no |
| @UPDATE@ | yes |
| @USE@ | yes |
| @USER@ | no |
| @USERS@ | no |
| @USING@ | yes |
| @UUID@ | no |
| @VALUES@ | no |
| @VARCHAR@ | no |
| @VARINT@ | no |
| @WHERE@ | yes |
| @WITH@ | yes |
| @WRITETIME@ | no |
| @DISTINCT@ | no |
h2(#changes). Changes
The following describes the addition/changes brought for each version of CQL.
h3. 3.1.4
* @CREATE INDEX@ now allows specifying options when creating CUSTOM indexes (see "CREATE INDEX reference":#createIndexStmt).
h3. 3.1.3
* Millisecond precision formats have been added to the timestamp parser (see "working with dates":#usingdates).
h3. 3.1.2
* @NaN@ and @Infinity@ has been added as valid float contants. They are now reserved keywords. In the unlikely case you we using them as a column identifier (or keyspace/table one), you will noew need to double quote them (see "quote identifiers":#identifiers).
h3. 3.1.1
* @SELECT@ statement now allows listing the partition keys (using the @DISTINCT@ modifier). See "CASSANDRA-4536":https://issues.apache.org/jira/browse/CASSANDRA-4536.
* The syntax @c IN ?@ is now supported in @WHERE@ clauses. In that case, the value expected for the bind variable will be a list of whatever type @c@ is.
* It is now possible to use named bind variables (using @:name@ instead of @?@).
h3. 3.1.0
* "ALTER TABLE":#alterTableStmt @DROP@ option has been reenabled for CQL3 tables and has new semantics now: the space formerly used by dropped columns will now be eventually reclaimed (post-compaction). You should not readd previously dropped columns unless you use timestamps with microsecond precision (see "CASSANDRA-3919":https://issues.apache.org/jira/browse/CASSANDRA-3919 for more details).
* @SELECT@ statement now supports aliases in select clause. Aliases in WHERE and ORDER BY clauses are not supported. See the "section on select"#selectStmt for details.
* @CREATE@ statements for @KEYSPACE@, @TABLE@ and @INDEX@ now supports an @IF NOT EXISTS@ condition. Similarly, @DROP@ statements support a @IF EXISTS@ condition.
* @INSERT@ statements optionally supports a @IF NOT EXISTS@ condition and @UPDATE@ supports @IF@ conditions.
h3. 3.0.5
* @SELECT@, @UPDATE@, and @DELETE@ statements now allow empty @IN@ relations (see "CASSANDRA-5626":https://issues.apache.org/jira/browse/CASSANDRA-5626).
h3. 3.0.4
* Updated the syntax for custom "secondary indexes":#createIndexStmt.
* Non-equal condition on the partition key are now never supported, even for ordering partitioner as this was not correct (the order was *not* the one of the type of the partition key). Instead, the @token@ method should always be used for range queries on the partition key (see "WHERE clauses":#selectWhere).
h3. 3.0.3
* Support for custom "secondary indexes":#createIndexStmt has been added.
h3. 3.0.2
* Type validation for the "constants":#constants has been fixed. For instance, the implementation used to allow @'2'@ as a valid value for an @int@ column (interpreting it has the equivalent of @2@), or @42@ as a valid @blob@ value (in which case @42@ was interpreted as an hexadecimal representation of the blob). This is no longer the case, type validation of constants is now more strict. See the "data types":#types section for details on which constant is allowed for which type.
* The type validation fixed of the previous point has lead to the introduction of "blobs constants":#constants to allow inputing blobs. Do note that while inputing blobs as strings constant is still supported by this version (to allow smoother transition to blob constant), it is now deprecated (in particular the "data types":#types section does not list strings constants as valid blobs) and will be removed by a future version. If you were using strings as blobs, you should thus update your client code ASAP to switch blob constants.
* A number of functions to convert native types to blobs have also been introduced. Furthermore the token function is now also allowed in select clauses. See the "section on functions":#functions for details.
h3. 3.0.1
* "Date strings":#usingdates (and timestamps) are no longer accepted as valid @timeuuid@ values. Doing so was a bug in the sense that date string are not valid @timeuuid@, and it was thus resulting in "confusing behaviors":https://issues.apache.org/jira/browse/CASSANDRA-4936. However, the following new methods have been added to help working with @timeuuid@: @now@, @minTimeuuid@, @maxTimeuuid@ , @dateOf@ and @unixTimestampOf@. See the "section dedicated to these methods":#usingtimeuuid for more detail.
* "Float constants"#constants now support the exponent notation. In other words, @4.2E10@ is now a valid floating point value.
h2. Versioning
Versioning of the CQL language adheres to the "Semantic Versioning":http://semver.org guidelines. Versions take the form X.Y.Z where X, Y, and Z are integer values representing major, minor, and patch level respectively. There is no correlation between Cassandra release versions and the CQL language version.
|_. version|_. description|
|Major |The major version _must_ be bumped when backward incompatible changes are introduced. This should rarely occur.|
|Minor |Minor version increments occur when new, but backward compatible, functionality is introduced.|
|Patch |The patch version is incremented when bugs are fixed.|
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