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The PostgreSQL 9.0 Reference Manual - Volume 1B - SQL Command Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 488 pages
ISBN 9781906966058
RRP £14.95 ($19.95)

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1.51 CREATE OPERATOR

Name

CREATE OPERATOR -- define a new operator

Synopsis

CREATE OPERATOR name (
    PROCEDURE = function_name
    [, LEFTARG = left_type ] [, RIGHTARG = right_type ]
    [, COMMUTATOR = com_op ] [, NEGATOR = neg_op ]
    [, RESTRICT = res_proc ] [, JOIN = join_proc ]
    [, HASHES ] [, MERGES ]
)

Description

CREATE OPERATOR defines a new operator, name. The user who defines an operator becomes its owner. If a schema name is given then the operator is created in the specified schema. Otherwise it is created in the current schema.

The operator name is a sequence of up to NAMEDATALEN-1 (63 by default) characters from the following list:

+ - * / < > = ~ ! @ # % ^ & | ` ?

There are a few restrictions on your choice of name:

The operator != is mapped to <> on input, so these two names are always equivalent.

At least one of LEFTARG and RIGHTARG must be defined. For binary operators, both must be defined. For right unary operators, only LEFTARG should be defined, while for left unary operators only RIGHTARG should be defined.

The function_name procedure must have been previously defined using CREATE FUNCTION and must be defined to accept the correct number of arguments (either one or two) of the indicated types.

The other clauses specify optional operator optimization clauses. Their meaning is detailed in Volume 2: Operator Optimization Information.

Parameters

name
The name of the operator to be defined. See above for allowable characters. The name can be schema-qualified, for example CREATE OPERATOR myschema.+ (...). If not, then the operator is created in the current schema. Two operators in the same schema can have the same name if they operate on different data types. This is called overloading.
function_name
The function used to implement this operator.
left_type
The data type of the operator's left operand, if any. This option would be omitted for a left-unary operator.
right_type
The data type of the operator's right operand, if any. This option would be omitted for a right-unary operator.
com_op
The commutator of this operator.
neg_op
The negator of this operator.
res_proc
The restriction selectivity estimator function for this operator.
join_proc
The join selectivity estimator function for this operator.
HASHES
Indicates this operator can support a hash join.
MERGES
Indicates this operator can support a merge join.

To give a schema-qualified operator name in com_op or the other optional arguments, use the OPERATOR() syntax, for example:

COMMUTATOR = OPERATOR(myschema.===) ,

Notes

Refer to Volume 2: User-Defined Operators for further information.

It is not possible to specify an operator's lexical precedence in CREATE OPERATOR, because the parser's precedence behavior is hard-wired. See Volume 1A: 2.1.6 Lexical Precedence for precedence details.

The obsolete options SORT1, SORT2, LTCMP, and GTCMP were formerly used to specify the names of sort operators associated with a merge-joinable operator. This is no longer necessary, since information about associated operators is found by looking at B-tree operator families instead. If one of these options is given, it is ignored except for implicitly setting MERGES true.

Use DROP OPERATOR to delete user-defined operators from a database. Use ALTER OPERATOR to modify operators in a database.

Examples

The following command defines a new operator, area-equality, for the data type box:

CREATE OPERATOR === (
    LEFTARG = box,
    RIGHTARG = box,
    PROCEDURE = area_equal_procedure,
    COMMUTATOR = ===,
    NEGATOR = !==,
    RESTRICT = area_restriction_procedure,
    JOIN = area_join_procedure,
    HASHES, MERGES
);

Compatibility

CREATE OPERATOR is a PostgreSQL extension. There are no provisions for user-defined operators in the SQL standard.

See Also

ALTER OPERATOR, CREATE OPERATOR CLASS, DROP OPERATOR

ISBN 9781906966058The PostgreSQL 9.0 Reference Manual - Volume 1B - SQL Command ReferenceSee the print edition