PolarDB:CREATE OPERATOR

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:

• -- and /* cannot appear anywhere in an operator name, since they will be taken as the start of a comment.

• A multicharacter operator name cannot end in + or -, unless the name also contains at least one of these characters:

  ~ ! @ # % ^ & | ` ?

  For example, @- is an allowed operator name, but *- is not. This restriction allows PolarDB to parse SQL-compliant commands without requiring spaces between tokens.

• The symbol => is reserved by the SQL grammar, so it cannot be used as an operator name.

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

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

Synopsis

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

Notes

The right unary operator (also known as suffix) has been deprecated.

The function_name function must have been previously defined using CREATE FUNCTION and must be defined to accept the correct number of arguments of the indicated types.

In the syntax of CREATE OPERATOR, the keywords FUNCTION and PROCEDURE are equivalent, but the referenced function must in any case be a function, not a procedure. The use of the keyword PROCEDURE here is historical and deprecated.

The other clauses specify optional operator optimization clauses. To be able to create an operator, you must have USAGE privilege on the argument types and the return type, as well as EXECUTE privilege on the underlying function. If a commutator or negator operator is specified, you must own these operators.

It is not possible to specify an operator's lexical precedence in CREATE OPERATOR, because the parser's precedence behavior is hard-wired.

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.

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 prefix operator.

right_type: The data type of the operator's right operand.

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.===) ,

Examples

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

    CREATE OPERATOR === (
        LEFTARG = box,
        RIGHTARG = box,
        FUNCTION = area_equal_function,
        COMMUTATOR = ===,
        NEGATOR = !==,
        RESTRICT = area_restriction_function,
        JOIN = area_join_function,
        HASHES, MERGES
    );