This reference covers CQL specification version 3.3.1¶
This section describes the statements supported by CQL to insert, update, delete and query data.
Querying data from data is done using a
select_statement ::= SELECT [ DISTINCT ] (
select_clause| '*' ) FROM
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 (*) AS user_count FROM users;
SELECT statement reads one or more columns for one or more rows in a table. It returns a result-set of the rows
matching the request, where each row contains the values for the selection corresponding to the query. Additionally,
functions including aggregation ones can be applied to the result.
SELECT statement contains at least a selection clause and the name of the table on which
the selection is on (note that CQL does not joins or sub-queries and thus a select statement only apply to a single
table). In most case, a select will also have a where clause and it can optionally have additional
clauses to order or limit the results. Lastly, queries that require
filtering can be allowed if the
ALLOW FILTERING flag is provided.
select_clause determines which columns needs to be queried and returned in the result-set, as well as any
transformation to apply to this result before returning. It consists of a comma-separated list of selectors or,
alternatively, of the wildcard character (
*) to select all the columns defined in the table.
selector can be one of:
- A column name of the table selected, to retrieve the values for that column.
- A term, which is usually used nested inside other selectors like functions (if a term is selected directly, then the corresponding column of the result-set will simply have the value of this term for every row returned).
- A casting, which allows you to convert a nested selector to a (compatible) type.
- A function call, where the arguments are selector themselves.
Every top-level selector can also be aliased (using AS). If so, the name of the corresponding column in the result set will be that of the alias. For instance:
// Without alias SELECT intAsBlob(4) FROM t; // intAsBlob(4) // -------------- // 0x00000004 // With alias SELECT intAsBlob(4) AS four FROM t; // four // ------------ // 0x00000004
Currently, aliases aren’t recognized anywhere else in the statement where they are used (not in the
clause, not in the
ORDER BY clause, …). You must use the orignal column name instead.
Selection supports two special functions (which aren’t allowed anywhere else):
TTL. Both functions
take only one argument and that argument must be a column name (so, for instance,
TTL(3) is invalid).
Those functions let you retrieve meta-information that is stored internally for each column, namely:
- the timestamp of the value of the column for
- the remaining time to live (in seconds) for the value of the column if it set to expire (and
WHERE clause specifies which rows must be queried. It is composed of relations on the columns that are part of
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 (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 restricted to the relations that let you select a contiguous (for the ordering) set of rows. For
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 query 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 yield a meaningful order. Also
note that ordering partitioners always orders token values by bytes (so even if the partition key is of type int,
token(-1) > token(0) in particular). For example:
SELECT * FROM posts WHERE token(userid) > token('tom') AND token(userid) < token('bob')
IN relation is only allowed on the last column of the partition key and on the last column of the full
It is also possible to “group”
CLUSTERING COLUMNS together in a relation using the tuple notation. For instance:
SELECT * FROM posts WHERE userid = 'john doe' AND (blog_title, posted_at) > ('John''s Blog', '2012-01-01')
will request all rows that sort after the one having “John’s Blog” as
blog_title and ‘2012-01-01’ for
in the clustering order. In particular, rows having a
post_at <= '2012-01-01' will be returned as long as their
blog_title > 'John''s Blog', which would not be the case for:
SELECT * FROM posts WHERE userid = 'john doe' AND blog_title > 'John''s Blog' AND posted_at > '2012-01-01'
The tuple notation may also be used for
IN clauses on clustering columns:
SELECT * FROM posts WHERE userid = 'john doe' AND (blog_title, posted_at) IN (('John''s Blog', '2012-01-01'), ('Extreme Chess', '2014-06-01'))
CONTAINS operator may only be used on collection columns (lists, sets, and maps). In the case of maps,
CONTAINS applies to the map values. The
CONTAINS KEY operator may only be used on map columns and applies to the
ORDER BY clause lets you 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
ASC). Currently the possible orderings are limited by the clustering order
defined on the table:
- if the table has been defined without any specific
CLUSTERING ORDER, then then allowed orderings are the order induced by the clustering columns and the reverse of that one.
- otherwise, the orderings allowed are the order of the
CLUSTERING ORDERoption and the reversed one.
LIMIT option to a
SELECT statement limits the number of rows returned by a query, while the
LIMIT option limits the number of rows returned for a given partition by the query. Note that both types of limit can
used in the same statement.
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
ALLOW FILTERING option lets you explicitly allow (some) queries that require filtering. Please note that a
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
For instance, consider 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 * FROM users WHERE birth_year = 1981;
because in both cases, Scylla guarantees that these queries’ performance will be proportional to the amount of data
returned. In particular, if no users were born in 1981, then the second query performance will not depend on the number
of user profiles stored in the database (not directly at least: due to secondary index implementation consideration, this
query may still depend on the number of nodes in the cluster, which indirectly depends on the amount of data stored.
Nevertheless, the number of nodes will always be multiple order of magnitude lower than the number of user profile
stored). Of course, both queries may return very large result sets in practice, but the amount of data returned can always
be controlled by adding a
However, the following query will be rejected:
SELECT * FROM users WHERE birth_year = 1981 AND country = 'FR';
because Scylla 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
FILTERING and so the following query is valid:
SELECT * FROM users WHERE birth_year = 1981 AND country = 'FR' ALLOW FILTERING;
Inserting data for a row is done using an
insert_statement: INSERT INTO `table_name` ( `names_values` ) : [ USING `update_parameter` ( AND `update_parameter` )* ] names_values: `names` VALUES `tuple_literal` names: '(' `column_name` ( ',' `column_name` )* ')'
INSERT INTO NerdMovies (movie, director, main_actor, year) VALUES ('Serenity', 'Joss Whedon', 'Nathan Fillion', 2005) USING TTL 86400;
INSERT statement writes one or more columns for a given row in a table. Note that since a row is identified by
PRIMARY KEY, at least the columns composing it must be specified. The list of columns to insert to must be
supplied when using the
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 means to know which of creation or update happened.
All updates for an
INSERT are applied atomically and in isolation.
Please refer to the UPDATE section for informations on the
Also note that
INSERT does not support counters, while
Updating a row is done using an
update_statement: UPDATE `table_name` : [ USING `update_parameter` ( AND `update_parameter` )* ] : SET `assignment` ( ',' `assignment` )* : WHERE `where_clause` : [ IF ( EXISTS | `condition` ( AND `condition` )*) ] update_parameter: ( TIMESTAMP | TTL ) ( `integer` | `bind_marker` ) assignment: `simple_selection` '=' `term` :| `column_name` '=' `column_name` ( '+' | '-' ) `term` :| `column_name` '=' `list_literal` '+' `column_name` simple_selection: `column_name` :| `column_name` '[' `term` ']' :| `column_name` '.' `field_name condition: `simple_selection` `operator` `term`
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';
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. Non primary key columns are then
set using the
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 way to know whether a creation or update occurred.
UPDATE statement, all updates within the same partition key are applied atomically and in isolation.
c = c + 3is used to increment/decrement counters. The column name after the ‘=’ sign must be the same as the one before the ‘=’ sign. Note that increment/decrement is only allowed on counters, and are the only update operations allowed on counters. See the section on counters for details.
id = id + <some-collection>and
id[value1] = value2are for collections, see the relevant section for details.
id.field = 3is for setting the value of a field on a non-frozen user-defined types.
BATCH for the
TIMESTAMP) statements support the following
TIMESTAMP: sets the timestamp for the operation. If not specified, the coordinator will use the current time (in microseconds) at the start of statement execution as the timestamp. This is usually a suitable default.
TTL: specifies 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 columns 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. A TTL of 0 is equivalent to no TTL. If the table has a default_time_to_live, a TTL of 0 will remove the TTL for the inserted or updated values. A TTL of
nullis equivalent to inserting with a TTL of 0.
Deleting rows or parts of rows uses the
delete_statement: DELETE [ `simple_selection` ( ',' `simple_selection` ) ] : FROM `table_name` : [ USING `update_parameter` ( AND `update_parameter` )* ] : WHERE `where_clause` : [ IF ( EXISTS | `condition` ( AND `condition` )*) ]
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);
DELETE statement deletes columns and rows. If column names are provided directly after the
only those columns are deleted from the row indicated by the
WHERE clause. Otherwise, whole rows are removed.
WHERE clause specifies which rows are to be deleted. Multiple rows may be deleted with one statement by using an
IN operator. A range of rows may be deleted using an inequality operator (such as
DELETE supports the
TIMESTAMP option with the same semantics as in updates.
DELETE statement, all deletions within the same partition key are applied atomically and in isolation.
DELETE operation can be conditional through the use of an
IF clause, similar to
statements. However, as with
UPDATE statements, this will incur a non-negligible performance cost
(internally, Paxos will be used) and so should be used sparingly.
DELETE can be executed in a single statement by grouping them through a
batch_statement: BEGIN [ UNLOGGED | COUNTER ] BATCH : [ USING `update_parameter` ( AND `update_parameter` )* ] : `modification_statement` ( ';' `modification_statement` )* : APPLY BATCH modification_statement: `insert_statement` | `update_statement` | `delete_statement`
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;
BATCH statement group multiple modification statements (insertions/updates and deletions) into a single
statement. It serves several 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
BATCHbelonging to a given partition key are performed in isolation.
- By default, all operations in the batch are performed as logged, to ensure all mutations eventually complete (or none will). See the notes on UNLOGGED batches for more details.
BATCHstatements may only contain
DELETEstatements (not other batches for instance).
- Batches are not a full analogue for SQL transactions.
- If a timestamp is not specified for each operation, then all operations will be applied with the same timestamp
(either one generated automatically, or the timestamp provided at the batch level). Due to Scylla’s conflict
resolution procedure in the case of timestamp ties, operations may
be applied in an order that is different from the order they are listed in the
BATCHstatement. To force a particular operation ordering, you must specify per-operation timestamps.
- A LOGGED batch to a single partition will be converted to an UNLOGGED batch as an optimization.
By default, Scylla uses a batch log to ensure all operations in a batch eventually complete or none will (note however that operations are 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 Scylla to skip the batchlog with the
UNLOGGED option. If the
UNLOGGED option is
used, a failed batch might leave the patch only partly applied.
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