What is Cassandra Query Language [CQL]

Cassandra Query Language (CQL)

The Cassandra Query Language “CQL” is language to communicate with the Cassandra database. It interact with Cassandra is using the CQL shell, cqlsh. Using cqlsh, you can create keyspaces and tables, insert and query tables etc.

I am going to share the basic rules, keywords, identifiers, constraints etc.

Identifiers and keywords

The CQL language uses identifiers to identify tables, columns and other objects. There is number of identifiers (like SELECT or ASC) are keywords. They have a fixed meaning for the language and most are reserved keyword for Cassandra database.

Identifiers and (unquoted) keywords are case insensitive. There is two type of identifiers i.e.

• unquoted_identifier :-   re('[a-zA-Z][a-zA-Z0-9_]*')
• quoted_identifier  :-   '"' (any character where " can appear if doubled)+ '"'

CQL Terms

CQL has the notion of a term that denotes the kind of values that CQL support. A term can be one of these

• Constant
• Literal
• function call
• type hint
• bind marker

Term	Values that CQL support
literal	collection_literal | udt_literal | tuple_literal
function_call	identifier '(' [ term (',' term)* ] ')'
type_hint	'(' cql_type `)` term
bind_marker	'?' | ':' identifier

CQL Constants

Following are the kind of constants in CQL

Constants	Defining Value
string	\'' (any character where ' can appear if doubled)+ '\''  '$$' (any character other than '$$') '$$'
integer	re('-?[0-9]+')
float	re('-?[0-9]+(\.[0-9]*)?([eE][+-]?[0-9+])?') | NAN | INFINITY
boolean	TRUE | FALSE
uuid	hex{8}-hex{4}-hex{4}-hex{4}-hex{12}
hex	re("[0-9a-fA-F]")
blob	'0' ('x' | 'X') hex+

Remark Point:-

• A string constant is an arbitrary sequence of characters enclosed by single-quote ('). Single-quote can be used without escaping ($$It's raining today$$).
• Integer, float and boolean constant are defined as expected. Note that the float allows NaN and Infinity constants.
• CQL supports UUID constants.
• Blobs content are provided in hexadecimal and prefixed by 0x.
• The special NULL constant denotes the absence of value.

CQL Comments

There is two type of comment in CQL that is below

1) Single-line comments:-

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

Example:-

-- This is a comment

// This is a comment too

2) Multi-line comments:-

Multi-line comments are also supported through enclosure within /* and */.

Example:-

/* this is a multi-line comment */

CQL Statements

CQL statements can be divided in the following categories:

• Data Definition statements
• Data Manipulation statements
• Secondary Indexes statements.
• Materialized Views statements.
• Database Roles and Permissions statements
• User-Defined Functions statements.
• User-Defined Types statements.
• Triggers statements.

CQL Statements categories	statement purpose
Data Definition statements	use_statement create_keyspace_statement alter_keyspace_statement drop_keyspace_statement create_table_statement alter_table_statement drop_table_statement truncate_statement
Data Manipulation statements	select_statement insert_statement update_statement delete_statement batch_statement
Secondary Indexes statements	create_index_statement drop_index_statement
Materialized Views statements	create_materialized_view_statement drop_materialized_view_statement
Database Roles and Permissions statements	create_role_statement alter_role_statement drop_role_statement grant_role_statement revoke_role_statement list_roles_statement grant_permission_statement revoke_permission_statement list_permissions_statement create_user_statement alter_user_statement drop_user_statement list_users_statement
User-Defined Functions statements	create_function_statement drop_function_statement create_aggregate_statement drop_aggregate_statement
User-Defined Types statements	create_type_statement alter_type_statement drop_type_statement
Triggers statements	create_trigger_statement drop_trigger_statement