Cassandra Query Language (CQL) v3.0.5

  1. Cassandra Query Language (CQL) v3.0.5
    1. CQL Syntax
      1. Preamble
      2. Conventions
      3. Identifiers and keywords
      4. Constants
      5. Comments
      6. Statements
      7. Prepared Statement
    2. Data Definition
      1. CREATE KEYSPACE
      2. USE
      3. ALTER KEYSPACE
      4. DROP KEYSPACE
      5. CREATE TABLE
      6. ALTER TABLE
      7. DROP TABLE
      8. TRUNCATE
      9. CREATE INDEX
      10. DROP INDEX
    3. Data Manipulation
      1. INSERT
      2. UPDATE
      3. DELETE
      4. BATCH
    4. Queries
      1. SELECT
    5. Data Types
      1. Working with dates
      2. Counters
      3. Working with collections
    6. Functions
      1. Token
      2. Timeuuid functions
      3. Blob conversion functions
    7. Appendix A: CQL Keywords
    8. Changes
      1. 3.0.5
      2. 3.0.4
      3. 3.0.3
      4. 3.0.2
      5. 3.0.1
    9. Versioning

CQL Syntax

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 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.

Conventions

To aid in specifying the CQL syntax, we will use the following conventions in this document:

<start> ::= TERMINAL <non-terminal1> <non-terminal1>
SELECT sample_usage FROM cql;

Identifiers and keywords

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-Z0-9_]*.

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.

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.

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-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.

Constants

CQL defines the following kind of constants: strings, integers, floats, booleans, uuids and blobs:

For how these constants are typed, see the data types section.

Comments

A comment in CQL is a line beginning by either double dashes (--) or double slash (//).

Multi-line comments are also supported through enclosure withing /* and */ (but nesting is not supported).

-- This is a comment
// This is a comment too
/* This is
   a multiline comment */

Statements

CQL consists of statements. As in SQL, these statements can be divided in 3 categories:

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:

<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> ::= '?'
      <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> )


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>.

The question mark (?) of <variable> is a bind variables for prepared statements.

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.

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 USE statement).

For supported <function>, see the section on functions.

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 bind variable marker (denoted by a ? symbol) 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 (values for bind variables must be provided in the order the bind variables are defined in the query string). 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.

Data Definition

CREATE KEYSPACE

Syntax:

<create-keyspace-stmt> ::= CREATE KEYSPACE <identifier> WITH <properties>


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;


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':

USE

Syntax:

<use-stmt> ::= USE <identifier>

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, until another USE statement is issued or the connection terminates.

ALTER KEYSPACE

Syntax:

<create-keyspace-stmt> ::= ALTER KEYSPACE <identifier> WITH <properties>


Sample:

ALTER KEYSPACE Excelsior
          WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 4};


The ALTER KEYSPACE statement alter the properties of an existing keyspace. The supported <properties> are the same that for the CREATE TABLE statement.

DROP KEYSPACE

Syntax:

<drop-keyspace-stmt> ::= DROP KEYSPACE <identifier>

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.

CREATE TABLE

Syntax:

<create-table-stmt> ::= CREATE (TABLE | COLUMNFAMILY) <tablename>
                          '(' <definition> ( ',' <definition> )* ')'
                          ( WITH <option> ( AND <option>)* )?

<column-definition> ::= <identifier> <type> ( PRIMARY KEY )?
                      | PRIMARY KEY '(' <partition-key> ( ',' <identifier> )* ')'

<partition-key> ::= <identifier>
                  | '(' <identifier> (',' <identifier> )* ')'

<option> ::= <property>
           | COMPACT STORAGE
           | CLUSTERING ORDER


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' };


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, it defines the columns composing rows of the table and have a number of options. Note that the CREATE COLUMNFAMILY syntax is supported as an alias for CREATE TABLE (for historical reasons).

<tablename>

Valid table names are the same than valid keyspace names (up to 32 characters long alphanumerical identifiers). If the table name is provided alone, the table is created within the current keyspace (see USE), but if it is prefixed by an existing keyspace name (see <tablename> grammar), it is created in the specified keyspace (but does not change the current keyspace).

<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 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:

CREATE TABLE t (
    k int PRIMARY KEY,
    other text
)

is equivalent to

CREATE TABLE t (
    k int,
    other text,
    PRIMARY KEY (k)
)

Partition key and clustering columns

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 SELECT).

<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 mainly targeted towards backward compatibility for definitions created before CQL3 (see www.datastax.com/dev/blog/thrift-to-cql3 for more details). The option also provides a slightly more compact layout of data on disk but at the price of diminished flexibility and extensibility for the table. Most notably, COMPACT STORAGE tables cannot have collections and a COMPACT STORAGE table with at least one clustering column supports exactly one (as in not 0 nor more than 1) column not part of the PRIMARY KEY definition (which imply in particular that you cannot add nor remove columns after creation). For those reasons, COMPACT STORAGE is not recommended outside of the backward compatibility reason evoked above.

Another option is CLUSTERING ORDER. It allows to define the ordering of rows on disk. It takes the list of the clustering column 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.

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 otpions 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.

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. 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 mininum 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.
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

Other considerations:

ALTER TABLE

Syntax:

<alter-table-stmt> ::= ALTER (TABLE | COLUMNFAMILY) <tablename> <instruction>

<instruction> ::= ALTER <identifier> TYPE <type>
                | ADD   <identifier> <type>
                | WITH  <option> ( AND <option> )*


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;


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:

Dropping a column is no yet supported but is on the roadmap. In the meantime, a declared but unused column has no impact on performance nor uses any storage.

DROP TABLE

Syntax:

<drop-table-stmt> ::= DROP TABLE <tablename>

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.

TRUNCATE

Syntax:

<truncate-stmt> ::= TRUNCATE <tablename>

Sample:

TRUNCATE superImportantData;

The TRUNCATE statement permanently removes all data from a table.

CREATE INDEX

Syntax:

<create-index-stmt> ::= CREATE ( CUSTOM )? INDEX <identifier>? ON <tablename> '(' <identifier> ')'
                                        ( USING <string> )?

Sample:

CREATE INDEX userIndex ON NerdMovies (user);
CREATE INDEX ON Mutants (abilityId);
CREATE CUSTOM INDEX ON users (email) USING 'path.to.the.IndexClass';

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 during the execution of this statement. After the index is created, new data for the column is indexed automatically at insertion time.

DROP INDEX

Syntax:

<drop-index-stmt> ::= DROP INDEX <identifier>

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.

Data Manipulation

INSERT

Syntax:

<insertStatement> ::= INSERT INTO <tablename>
                             '(' <identifier> ( ',' <identifier> )* ')'
                      VALUES '(' <term-or-literal> ( ',' <term-or-literal> )* ')'
                      ( USING <option> ( AND <option> )* )?

<term-or-literal> ::= <term>
                    | <collection-literal>

<option> ::= TIMESTAMP <integer>
           | TTL <integer>


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, at least the columns composing it must be specified.

Note that unlike in SQL, INSERT does not check the prior existence of the row: the row is created if none existed before, and updated otherwise. Furthermore, there is no mean to know which of creation or update happened. In fact, the semantic of INSERT and UPDATE are identical.

All updates for an INSERT are applied atomically and in isolation.

Please refer to the UPDATE section for information on the <option> available and to the collections section for use of <collection-literal>. Also note that INSERT does not support counters, while UPDATE does.

UPDATE

Syntax:

<update-stmt> ::= UPDATE <tablename>
                  ( USING <option> ( AND <option> )* )?
                  SET <assignment> ( ',' <assignment> )*
                  WHERE <where-clause>

<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> )* )? ')'

<option> ::= TIMESTAMP <integer>
           | TTL <integer>


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';


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: the row is created if none existed before, and updated otherwise. Furthermore, there is no mean to know which of creation or update happened. In fact, the semantic of INSERT and UPDATE are identical.

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 for more details.

<options>

The UPDATE and INSERT statements allows to specify the following options for the insertion:

DELETE

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> )* )? ')'


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);


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 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 statement.

In a DELETE statement, all deletions within the same partition key are applied atomically and in isolation.

BATCH

Syntax:

<batch-stmt> ::= BEGIN ( UNLOGGED | COUNTER ) BATCH
                 ( USING <option> ( AND <option> )* )?
                    <modification-stmt> ( ';' <modification-stmt> )*
                 APPLY BATCH

<modification-stmt> ::= <insert-stmt>
                      | <update-stmt>
                      | <delete-stmt>

<option> ::= TIMESTAMP <integer>


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 serves several purposes:

  1. It saves network round-trips between the client and the server (and sometimes between the server coordinator and the replicas) when batching multiple updates.
  2. All updates in a BATCH belonging to a given partition key are performed in isolation.
  3. By default, all operations in the batch are performed atomically. See the notes on UNLOGGED for more details.

Note however that the BATCH statement only allows UPDATE, INSERT and DELETE statements and is not a full analogue for SQL transactions.

UNLOGGED

By default, Cassandra uses a batch log to ensure all operations in a batch are applied atomically. (Note that the operations are still only isolated within a single partition.)

There is a performance penalty for batch atomicity when a batch spans multiple partitions. If you do not want to incur this penalty, you can tell Cassandra to skip the batchlog with the UNLOGGED option. If the UNLOGGED option is used, operations are only atomic within a single partition.

COUNTER

Use the COUNTER option for batched counter updates. Unlike other updates in Cassandra, counter updates are not idempotent.

<option>

BATCH supports both the TIMESTAMP option, with similar semantic to the one described in the UPDATE 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.

Queries

SELECT

Syntax:

<select-stmt> ::= SELECT <select-clause>
                  FROM <tablename>
                  ( WHERE <where-clause> )?
                  ( ORDER BY <order-by> )?
                  ( LIMIT <integer> )?
                  ( ALLOW FILTERING )?

<select-clause> ::= <selection-list>
                  | COUNT '(' ( '*' | '1' ) ')'

<selection-list> ::= <selector> ( ',' <selector> )*
                   | '*'

<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 )?


Sample:

SELECT name, occupation FROM users WHERE userid IN (199, 200, 207);

SELECT time, value
FROM events
WHERE event_type = 'myEvent'
  AND time > '2011-02-03'
  AND time <= '2012-01-01'

SELECT COUNT(*) FROM users;


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.

<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 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. 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)).

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.

<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 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

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:

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):

// 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 yeld 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:

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.

<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):

LIMIT

The LIMIT option to a SELECT statement limits the number of rows returned by a query.

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 explicitely 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:

CREATE TABLE users (
    username text PRIMARY KEY,
    firstname text,
    lastname text,
    birth_year int,
    country text
)

CREATE INDEX ON users(birth_year);

Then the following queries are valid:

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 2ndary 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:

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:

SELECT firstname, lastname FROM users WHERE birth_year = 1981 AND country = 'FR' ALLOW FILTERING;

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:

<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> '>'

Note that the native types are keywords and as such are case-insensitive. They are however not reserved ones.

The following table gives additional informations on the native data types, and on which kind of constants each type supports:

type constants supporteddescription
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 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 below for more information.
timeuuid uuids Type 1 UUID. This is generally used as a “conflict-free” timestamp. Also see the functions on Timeuuid
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 section below.

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.:

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.

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:

In that case, the time of day will default to 00:00:00, in the specified or default time zone.

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 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 for more information).

The use of the counter type is limited in the following way:

Working with collections

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:

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.

Maps

A map is a typed 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:

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.

// 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:

// 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,

// 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:

DELETE favs['author'] FROM users WHERE id = 'jsmith'

Sets

A set is a typed 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:

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.

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.

UPDATE images SET tags = tags + { 'cute', 'cuddly' } WHERE name = 'cat.jpg';
UPDATE images SET tags = tags - { 'lame' } WHERE name = 'cat.jpg';

As with maps, TTLs if used only apply to the newly inserted/updated values.

Lists

A list is a typed 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:

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 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.

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.

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:

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 occurences of 12 and 21 from scores

As with maps, TTLs if used only apply to the newly inserted/updated values.

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:

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 instance, in a cluster using the default Murmur3Partitioner, if a table is defined by

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 columns so the partition key is the same than the primary key)), and the return type will be bigint.

Timeuuid functions

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

SELECT * FROM myTable WHERE t = now()

will never return any result by design, since the value returned by now() is guaranteed to be unique.

minTimeuuid and maxTimeuuid

The minTimeuuid (resp. maxTimeuuid) function takes a timestamp value t (which can be either a timestamp or a date string) and return a fake timeuuid corresponding to the smallest (resp. biggest) possible timeuuid having for timestamp t. So for instance:

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 stricly 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. 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.

dateOf and unixTimestampOf

The dateOf and unixTimestampOf functions take a timeuuid argument and extract the embeded 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.

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.

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'ĂȘtre 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
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

Changes

The following describes the addition/changes brought for each version of CQL.

3.0.5

3.0.4

3.0.3

3.0.2

3.0.1

Versioning

Versioning of the CQL language adheres to the Semantic Versioning 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.

versiondescription
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.