Postgresql 中文操作指南

CREATE OPERATOR CLASS

CREATE OPERATOR CLASS - 定义一个新的运算符类

CREATE OPERATOR CLASS — define a new operator class

Synopsis

CREATE OPERATOR CLASS name [ DEFAULT ] FOR TYPE data_type
  USING index_method [ FAMILY family_name ] AS
  {  OPERATOR strategy_number operator_name [ ( op_type, op_type ) ] [ FOR SEARCH | FOR ORDER BY sort_family_name ]
   | FUNCTION support_number [ ( op_type [ , op_type ] ) ] function_name ( argument_type [, ...] )
   | STORAGE storage_type
  } [, ... ]

Description

CREATE OPERATOR CLASS 创建一个新的运营商类。运算符类定义了如何使用特定数据类型与索引。运算符类指定某些运算符将为该数据类型和索引方法填充特定角色或“策略”。运算符类还指定索引方法在为索引列选择运算符类时要使用的支持函数。在创建运算符类之前，必须定义运算符类使用的所有运算符和函数。

CREATE OPERATOR CLASS creates a new operator class. An operator class defines how a particular data type can be used with an index. The operator class specifies that certain operators will fill particular roles or “strategies” for this data type and this index method. The operator class also specifies the support functions to be used by the index method when the operator class is selected for an index column. All the operators and functions used by an operator class must be defined before the operator class can be created.

如果给出了模式名称，则在指定的模式中创建运算符类。否则，它将在当前模式中创建。同模式中的两个运算符类仅当针对不同的索引方法时才能具有相同的名称。

If a schema name is given then the operator class is created in the specified schema. Otherwise it is created in the current schema. Two operator classes in the same schema can have the same name only if they are for different index methods.

定义运算符类的用户将成为其所有者。目前，创建用户必须是超级用户。（此限制的目的是由于错误的运算符类定义可能会混淆甚至使服务器崩溃。）

The user who defines an operator class becomes its owner. Presently, the creating user must be a superuser. (This restriction is made because an erroneous operator class definition could confuse or even crash the server.)

CREATE OPERATOR CLASS 目前不检查运算符类定义是否包含索引方法所需的所有运算符和函数，也不检查运算符和函数是否形成自洽的集合。定义有效的运算符类是用户的责任。

CREATE OPERATOR CLASS does not presently check whether the operator class definition includes all the operators and functions required by the index method, nor whether the operators and functions form a self-consistent set. It is the user’s responsibility to define a valid operator class.

相关的运算符类可以分组到 operator families 中。要将新的运算符类添加到现有系列中，请在其 CREATE OPERATOR CLASS 中指定 FAMILY 选项。如果没有此选项，则新类将放入一个与新类同名的系列中（如果它不存在，则会创建该系列）。

Related operator classes can be grouped into operator families. To add a new operator class to an existing family, specify the FAMILY option in CREATE OPERATOR CLASS. Without this option, the new class is placed into a family named the same as the new class (creating that family if it doesn’t already exist).

有关更多信息，请参阅 Section 38.16 。

Refer to Section 38.16 for further information.

Parameters

  • name

    • The name of the operator class to be created. The name can be schema-qualified.

  • DEFAULT

    • If present, the operator class will become the default operator class for its data type. At most one operator class can be the default for a specific data type and index method.

  • data_type

    • The column data type that this operator class is for.

  • index_method

    • The name of the index method this operator class is for.

  • family_name

    • The name of the existing operator family to add this operator class to. If not specified, a family named the same as the operator class is used (creating it, if it doesn’t already exist).

  • strategy_number

    • The index method’s strategy number for an operator associated with the operator class.

  • operator_name

    • The name (optionally schema-qualified) of an operator associated with the operator class.

  • op_type

    • In an OPERATOR clause, the operand data type(s) of the operator, or NONE to signify a prefix operator. The operand data types can be omitted in the normal case where they are the same as the operator class’s data type.

    • In a FUNCTION clause, the operand data type(s) the function is intended to support, if different from the input data type(s) of the function (for B-tree comparison functions and hash functions) or the class’s data type (for B-tree sort support functions, B-tree equal image functions, and all functions in GiST, SP-GiST, GIN and BRIN operator classes). These defaults are correct, and so op_type need not be specified in FUNCTION clauses, except for the case of a B-tree sort support function that is meant to support cross-data-type comparisons.

  • sort_family_name

    • The name (optionally schema-qualified) of an existing btree operator family that describes the sort ordering associated with an ordering operator.

    • If neither FOR SEARCH nor FOR ORDER BY is specified, FOR SEARCH is the default.

  • support_number

    • The index method’s support function number for a function associated with the operator class.

  • function_name

    • The name (optionally schema-qualified) of a function that is an index method support function for the operator class.

  • argument_type

    • The parameter data type(s) of the function.

  • storage_type

    • The data type actually stored in the index. Normally this is the same as the column data type, but some index methods (currently GiST, GIN, SP-GiST and BRIN) allow it to be different. The STORAGE clause must be omitted unless the index method allows a different type to be used. If the column data_type is specified as anyarray, the storage_type can be declared as anyelement to indicate that the index entries are members of the element type belonging to the actual array type that each particular index is created for.

OPERATOR 、 FUNCTION 和 STORAGE 子句可以按任何顺序出现。

The OPERATOR, FUNCTION, and STORAGE clauses can appear in any order.

Notes

由于索引机制在使用函数之前不会检查函数的访问权限，因此在操作符类中包含函数或操作符等同于授予对其公共执行权限。对于在操作符类中很有用的函数类型通常这不是问题。

Because the index machinery does not check access permissions on functions before using them, including a function or operator in an operator class is tantamount to granting public execute permission on it. This is usually not an issue for the sorts of functions that are useful in an operator class.

运算符不应由 SQL 函数定义。SQL 函数可能会内联到调用查询中，这将阻止优化器识别查询是否匹配某个索引。

The operators should not be defined by SQL functions. An SQL function is likely to be inlined into the calling query, which will prevent the optimizer from recognizing that the query matches an index.

在 PostgreSQL 8.4 之前， OPERATOR 子句可以包含 RECHECK 选项。不再支持此选项，因为索引运算符是“有损”的，现在在运行时动态确定。这允许高效处理运算符可能是有损或无损的情况。

Before PostgreSQL 8.4, the OPERATOR clause could include a RECHECK option. This is no longer supported because whether an index operator is “lossy” is now determined on-the-fly at run time. This allows efficient handling of cases where an operator might or might not be lossy.

Examples

以下示例命令定义了数据类型 _int4 （ int4 的数组）的 GiST 索引操作符类。请参阅 intarray 模块以了解完整示例。

The following example command defines a GiST index operator class for the data type _int4 (array of int4). See the intarray module for the complete example.

CREATE OPERATOR CLASS gist__int_ops
    DEFAULT FOR TYPE _int4 USING gist AS
        OPERATOR        3       &&,
        OPERATOR        6       = (anyarray, anyarray),
        OPERATOR        7       @>,
        OPERATOR        8       <@,
        OPERATOR        20      @@ (_int4, query_int),
        FUNCTION        1       g_int_consistent (internal, _int4, smallint, oid, internal),
        FUNCTION        2       g_int_union (internal, internal),
        FUNCTION        3       g_int_compress (internal),
        FUNCTION        4       g_int_decompress (internal),
        FUNCTION        5       g_int_penalty (internal, internal, internal),
        FUNCTION        6       g_int_picksplit (internal, internal),
        FUNCTION        7       g_int_same (_int4, _int4, internal);

Compatibility

CREATE OPERATOR CLASS 是 PostgreSQL 扩展。SQL 标准中没有 CREATE OPERATOR CLASS 语句。

CREATE OPERATOR CLASS is a PostgreSQL extension. There is no CREATE OPERATOR CLASS statement in the SQL standard.

See Also

ALTER OPERATOR CLASS ， DROP OPERATOR CLASS ， CREATE OPERATOR FAMILY ， ALTER OPERATOR FAMILY

ALTER OPERATOR CLASS, DROP OPERATOR CLASS, CREATE OPERATOR FAMILY, ALTER OPERATOR FAMILY