Postgresql 中文操作指南

CREATE FUNCTION

CREATE FUNCTION — 定义新函数

CREATE FUNCTION — define a new function

Synopsis

CREATE [ OR REPLACE ] FUNCTION
    name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } default_expr ] [, ...] ] )
    [ RETURNS rettype
      | RETURNS TABLE ( column_name column_type [, ...] ) ]
  { LANGUAGE lang_name
    | TRANSFORM { FOR TYPE type_name } [, ... ]
    | WINDOW
    | { IMMUTABLE | STABLE | VOLATILE }
    | [ NOT ] LEAKPROOF
    | { CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT }
    | { [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER }
    | PARALLEL { UNSAFE | RESTRICTED | SAFE }
    | COST execution_cost
    | ROWS result_rows
    | SUPPORT support_function
    | SET configuration_parameter { TO value | = value | FROM CURRENT }
    | AS 'definition'
    | AS 'obj_file', 'link_symbol'
    | sql_body
  } ...

Description

CREATE FUNCTION 定义了一个新函数。 CREATE OR REPLACE FUNCTION 将创建一个新函数或替换现有定义。为了能够定义函数，用户必须具有该语言的 USAGE 权限。

CREATE FUNCTION defines a new function. CREATE OR REPLACE FUNCTION will either create a new function, or replace an existing definition. To be able to define a function, the user must have the USAGE privilege on the language.

如果包括模式名称，则会在指定的模式中创建函数。否则，它将在当前模式中创建。新函数的名称不得与在同一模式中具有相同输入参数类型的任何现有函数或过程匹配。但是，具有不同参数类型的函数和过程可以共享名称（这称为 overloading ）。

If a schema name is included, then the function is created in the specified schema. Otherwise it is created in the current schema. The name of the new function must not match any existing function or procedure with the same input argument types in the same schema. However, functions and procedures of different argument types can share a name (this is called overloading).

要替换现有函数的当前定义，请使用 CREATE OR REPLACE FUNCTION 。通过这种方式无法更改函数的名称或参数类型（如果您尝试，实际上将创建独立的新函数）。此外， CREATE OR REPLACE FUNCTION 不允许您更改现有函数的返回类型。要做到这一点，您必须删除并重新创建该函数。（当使用 OUT 参数时，这意味着您只能通过删除函数来更改 OUT 参数的类型。）

To replace the current definition of an existing function, use CREATE OR REPLACE FUNCTION. It is not possible to change the name or argument types of a function this way (if you tried, you would actually be creating a new, distinct function). Also, CREATE OR REPLACE FUNCTION will not let you change the return type of an existing function. To do that, you must drop and recreate the function. (When using OUT parameters, that means you cannot change the types of any OUT parameters except by dropping the function.)

当 CREATE OR REPLACE FUNCTION 用于替换现有函数时，函数的所有权和权限不会改变。函数的其他所有属性都会被分配为命令中指定或隐含的值。您必须拥有该函数才能替换它（包括成为所有角色的成员）。

When CREATE OR REPLACE FUNCTION is used to replace an existing function, the ownership and permissions of the function do not change. All other function properties are assigned the values specified or implied in the command. You must own the function to replace it (this includes being a member of the owning role).

如果您删除并重新创建了一个函数，那么新函数与旧函数不是同一实体；您将必须删除引用旧函数的现有规则、视图、触发器等等。使用 CREATE OR REPLACE FUNCTION 更改函数定义，而不会中断引用该函数的对象。此外， ALTER FUNCTION 可用于更改现有函数的大部分辅助属性。

If you drop and then recreate a function, the new function is not the same entity as the old; you will have to drop existing rules, views, triggers, etc. that refer to the old function. Use CREATE OR REPLACE FUNCTION to change a function definition without breaking objects that refer to the function. Also, ALTER FUNCTION can be used to change most of the auxiliary properties of an existing function.

创建函数的用户成为该函数的所有者。

The user that creates the function becomes the owner of the function.

要能够创建函数，您必须对参数类型和返回类型具有 USAGE 权限。

To be able to create a function, you must have USAGE privilege on the argument types and the return type.

请参阅 Section 38.3 了解更多有关编写函数的信息。

Refer to Section 38.3 for further information on writing functions.

Parameters

  • name

    • The name (optionally schema-qualified) of the function to create.

  • argmode

    • The mode of an argument: IN, OUT, INOUT, or VARIADIC. If omitted, the default is IN. Only OUT arguments can follow a VARIADIC one. Also, OUT and INOUT arguments cannot be used together with the RETURNS TABLE notation.

  • argname

    • The name of an argument. Some languages (including SQL and PL/pgSQL) let you use the name in the function body. For other languages the name of an input argument is just extra documentation, so far as the function itself is concerned; but you can use input argument names when calling a function to improve readability (see Section 4.3). In any case, the name of an output argument is significant, because it defines the column name in the result row type. (If you omit the name for an output argument, the system will choose a default column name.)

  • argtype

    • The data type(s) of the function’s arguments (optionally schema-qualified), if any. The argument types can be base, composite, or domain types, or can reference the type of a table column.

    • Depending on the implementation language it might also be allowed to specify “pseudo-types” such as cstring. Pseudo-types indicate that the actual argument type is either incompletely specified, or outside the set of ordinary SQL data types.

    • The type of a column is referenced by writing _table_name.column_name%TYPE_. Using this feature can sometimes help make a function independent of changes to the definition of a table.

  • default_expr

    • An expression to be used as default value if the parameter is not specified. The expression has to be coercible to the argument type of the parameter. Only input (including INOUT) parameters can have a default value. All input parameters following a parameter with a default value must have default values as well.

  • rettype

    • The return data type (optionally schema-qualified). The return type can be a base, composite, or domain type, or can reference the type of a table column. Depending on the implementation language it might also be allowed to specify “pseudo-types” such as cstring. If the function is not supposed to return a value, specify void as the return type.

    • When there are OUT or INOUT parameters, the RETURNS clause can be omitted. If present, it must agree with the result type implied by the output parameters: RECORD if there are multiple output parameters, or the same type as the single output parameter.

    • The SETOF modifier indicates that the function will return a set of items, rather than a single item.

    • The type of a column is referenced by writing _table_name.column_name%TYPE_.

  • column_name

    • The name of an output column in the RETURNS TABLE syntax. This is effectively another way of declaring a named OUT parameter, except that RETURNS TABLE also implies RETURNS SETOF.

  • column_type

    • The data type of an output column in the RETURNS TABLE syntax.

  • lang_name

    • The name of the language that the function is implemented in. It can be sql, c, internal, or the name of a user-defined procedural language, e.g., plpgsql. The default is sql if sql_body is specified. Enclosing the name in single quotes is deprecated and requires matching case.

  • TRANSFORM { FOR TYPE _type_name } [, …​ ] }_

    • Lists which transforms a call to the function should apply. Transforms convert between SQL types and language-specific data types; see CREATE TRANSFORM. Procedural language implementations usually have hardcoded knowledge of the built-in types, so those don’t need to be listed here. If a procedural language implementation does not know how to handle a type and no transform is supplied, it will fall back to a default behavior for converting data types, but this depends on the implementation.

  • WINDOW

    • WINDOW indicates that the function is a window function rather than a plain function. This is currently only useful for functions written in C. The WINDOW attribute cannot be changed when replacing an existing function definition.

  • IMMUTABLE_STABLE_VOLATILE

    • These attributes inform the query optimizer about the behavior of the function. At most one choice can be specified. If none of these appear, VOLATILE is the default assumption.

    • IMMUTABLE indicates that the function cannot modify the database and always returns the same result when given the same argument values; that is, it does not do database lookups or otherwise use information not directly present in its argument list. If this option is given, any call of the function with all-constant arguments can be immediately replaced with the function value.

    • STABLE indicates that the function cannot modify the database, and that within a single table scan it will consistently return the same result for the same argument values, but that its result could change across SQL statements. This is the appropriate selection for functions whose results depend on database lookups, parameter variables (such as the current time zone), etc. (It is inappropriate for AFTER triggers that wish to query rows modified by the current command.) Also note that the current_timestamp family of functions qualify as stable, since their values do not change within a transaction.

    • VOLATILE indicates that the function value can change even within a single table scan, so no optimizations can be made. Relatively few database functions are volatile in this sense; some examples are random(), currval(), timeofday(). But note that any function that has side-effects must be classified volatile, even if its result is quite predictable, to prevent calls from being optimized away; an example is setval().

    • For additional details see Section 38.7.

  • LEAKPROOF

    • LEAKPROOF indicates that the function has no side effects. It reveals no information about its arguments other than by its return value. For example, a function which throws an error message for some argument values but not others, or which includes the argument values in any error message, is not leakproof. This affects how the system executes queries against views created with the security_barrier option or tables with row level security enabled. The system will enforce conditions from security policies and security barrier views before any user-supplied conditions from the query itself that contain non-leakproof functions, in order to prevent the inadvertent exposure of data. Functions and operators marked as leakproof are assumed to be trustworthy, and may be executed before conditions from security policies and security barrier views. In addition, functions which do not take arguments or which are not passed any arguments from the security barrier view or table do not have to be marked as leakproof to be executed before security conditions. See CREATE VIEW and Section 41.5. This option can only be set by the superuser.

  • CALLED ON NULL INPUT_RETURNS NULL ON NULL INPUT_STRICT

    • CALLED ON NULL INPUT (the default) indicates that the function will be called normally when some of its arguments are null. It is then the function author’s responsibility to check for null values if necessary and respond appropriately.

    • RETURNS NULL ON NULL INPUT or STRICT indicates that the function always returns null whenever any of its arguments are null. If this parameter is specified, the function is not executed when there are null arguments; instead a null result is assumed automatically.

  • [EXTERNAL] SECURITY INVOKER_[EXTERNAL] SECURITY DEFINER_

    • SECURITY INVOKER indicates that the function is to be executed with the privileges of the user that calls it. That is the default. SECURITY DEFINER specifies that the function is to be executed with the privileges of the user that owns it. For information on how to write SECURITY DEFINER functions safely, see below.

    • The key word EXTERNAL is allowed for SQL conformance, but it is optional since, unlike in SQL, this feature applies to all functions not only external ones.

  • PARALLEL

    • PARALLEL UNSAFE indicates that the function can’t be executed in parallel mode and the presence of such a function in an SQL statement forces a serial execution plan. This is the default. PARALLEL RESTRICTED indicates that the function can be executed in parallel mode, but the execution is restricted to parallel group leader. PARALLEL SAFE indicates that the function is safe to run in parallel mode without restriction.

    • Functions should be labeled parallel unsafe if they modify any database state, or if they make changes to the transaction such as using sub-transactions, or if they access sequences or attempt to make persistent changes to settings (e.g., setval). They should be labeled as parallel restricted if they access temporary tables, client connection state, cursors, prepared statements, or miscellaneous backend-local state which the system cannot synchronize in parallel mode (e.g., setseed cannot be executed other than by the group leader because a change made by another process would not be reflected in the leader). In general, if a function is labeled as being safe when it is restricted or unsafe, or if it is labeled as being restricted when it is in fact unsafe, it may throw errors or produce wrong answers when used in a parallel query. C-language functions could in theory exhibit totally undefined behavior if mislabeled, since there is no way for the system to protect itself against arbitrary C code, but in most likely cases the result will be no worse than for any other function. If in doubt, functions should be labeled as UNSAFE, which is the default.

  • COST execution_cost

    • A positive number giving the estimated execution cost for the function, in units of cpu_operator_cost. If the function returns a set, this is the cost per returned row. If the cost is not specified, 1 unit is assumed for C-language and internal functions, and 100 units for functions in all other languages. Larger values cause the planner to try to avoid evaluating the function more often than necessary.

  • ROWS result_rows

    • A positive number giving the estimated number of rows that the planner should expect the function to return. This is only allowed when the function is declared to return a set. The default assumption is 1000 rows.

  • SUPPORT support_function

    • The name (optionally schema-qualified) of a planner support function to use for this function. See Section 38.11 for details. You must be superuser to use this option.

  • configuration_parameter__value

    • The SET clause causes the specified configuration parameter to be set to the specified value when the function is entered, and then restored to its prior value when the function exits. SET FROM CURRENT saves the value of the parameter that is current when CREATE FUNCTION is executed as the value to be applied when the function is entered.

    • If a SET clause is attached to a function, then the effects of a SET LOCAL command executed inside the function for the same variable are restricted to the function: the configuration parameter’s prior value is still restored at function exit. However, an ordinary SET command (without LOCAL) overrides the SET clause, much as it would do for a previous SET LOCAL command: the effects of such a command will persist after function exit, unless the current transaction is rolled back.

    • See SET and Chapter 20 for more information about allowed parameter names and values.

  • definition

    • A string constant defining the function; the meaning depends on the language. It can be an internal function name, the path to an object file, an SQL command, or text in a procedural language.

    • It is often helpful to use dollar quoting (see Section 4.1.2.4) to write the function definition string, rather than the normal single quote syntax. Without dollar quoting, any single quotes or backslashes in the function definition must be escaped by doubling them.

  • obj_file_, _link_symbol

    • This form of the AS clause is used for dynamically loadable C language functions when the function name in the C language source code is not the same as the name of the SQL function. The string obj_file is the name of the shared library file containing the compiled C function, and is interpreted as for the LOAD command. The string link_symbol is the function’s link symbol, that is, the name of the function in the C language source code. If the link symbol is omitted, it is assumed to be the same as the name of the SQL function being defined. The C names of all functions must be different, so you must give overloaded C functions different C names (for example, use the argument types as part of the C names).

    • When repeated CREATE FUNCTION calls refer to the same object file, the file is only loaded once per session. To unload and reload the file (perhaps during development), start a new session.

  • sql_body

    • The body of a LANGUAGE SQL function. This can either be a single statement

RETURN expression

  • or a block

BEGIN ATOMIC
  statement;
  statement;
  ...
  statement;
END

  • This is similar to writing the text of the function body as a string constant (see definition above), but there are some differences: This form only works for LANGUAGE SQL, the string constant form works for all languages. This form is parsed at function definition time, the string constant form is parsed at execution time; therefore this form cannot support polymorphic argument types and other constructs that are not resolvable at function definition time. This form tracks dependencies between the function and objects used in the function body, so DROP …​ CASCADE will work correctly, whereas the form using string literals may leave dangling functions. Finally, this form is more compatible with the SQL standard and other SQL implementations.

Overloading

PostgreSQL 允许函数 overloading ；也就是说，同一个名称可以用于几个不同的函数，只要它们的输入参数类型不同即可。无论您是否使用它，这种能力在数据库中调用函数时都会带来安全预防措施，其中一些用户不信任其他用户；请参见 Section 10.3 。

PostgreSQL allows function overloading; that is, the same name can be used for several different functions so long as they have distinct input argument types. Whether or not you use it, this capability entails security precautions when calling functions in databases where some users mistrust other users; see Section 10.3.

如果两个函数具有相同名称和 input 参数类型，则认为这两个函数是相同的，忽略任何 OUT 参数。因此，例如，这些声明相互冲突：

Two functions are considered the same if they have the same names and input argument types, ignoring any OUT parameters. Thus for example these declarations conflict:

CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, out text) ...

具有不同参数类型列表的函数在创建时将不被视为冲突，但如果提供了默认值，它们可能会在使用中冲突。例如，考虑

Functions that have different argument type lists will not be considered to conflict at creation time, but if defaults are provided they might conflict in use. For example, consider

CREATE FUNCTION foo(int) ...
CREATE FUNCTION foo(int, int default 42) ...

调用 foo(10) 会失败，因为无法确定应该调用哪个函数。

A call foo(10) will fail due to the ambiguity about which function should be called.

Notes

完整的 SQL 类型语法允许声明函数的参数和返回值。但是，带括号的类型修饰符（例如，类型 numeric 的精度字段）会被 CREATE FUNCTION 丢弃。因此，例如， CREATE FUNCTION foo (varchar(10)) …​ 与 CREATE FUNCTION foo (varchar) …​ 完全相同。

The full SQL type syntax is allowed for declaring a function’s arguments and return value. However, parenthesized type modifiers (e.g., the precision field for type numeric) are discarded by CREATE FUNCTION. Thus for example CREATE FUNCTION foo (varchar(10)) …​ is exactly the same as CREATE FUNCTION foo (varchar) …​.

在 CREATE OR REPLACE FUNCTION 中用现有的函数替换现有函数时，对更改参数名称有一些限制。您无法更改已分配给任何输入参数的名称（尽管您可以向以前没有名称的参数添加名称）。如果有多个输出参数，则不能更改输出参数的名称，因为这会更改描述函数结果的匿名复合类型的列名称。这些限制是为了确保在替换函数时，对函数的现有调用不会停止工作。

When replacing an existing function with CREATE OR REPLACE FUNCTION, there are restrictions on changing parameter names. You cannot change the name already assigned to any input parameter (although you can add names to parameters that had none before). If there is more than one output parameter, you cannot change the names of the output parameters, because that would change the column names of the anonymous composite type that describes the function’s result. These restrictions are made to ensure that existing calls of the function do not stop working when it is replaced.

如果用 VARIADIC 参数声明函数 STRICT ，则严格性检查会测试变长数组 as a whole 是否为非空。如果该数组具有空元素，则仍将调用该函数。

If a function is declared STRICT with a VARIADIC argument, the strictness check tests that the variadic array as a whole is non-null. The function will still be called if the array has null elements.

Examples

使用 SQL 函数添加两个整数：

Add two integers using an SQL function:

CREATE FUNCTION add(integer, integer) RETURNS integer
    AS 'select $1 + $2;'
    LANGUAGE SQL
    IMMUTABLE
    RETURNS NULL ON NULL INPUT;

使用参数名称和未加引号的主体编写的以更符合 SQL 的样式编写的相同函数：

The same function written in a more SQL-conforming style, using argument names and an unquoted body:

CREATE FUNCTION add(a integer, b integer) RETURNS integer
    LANGUAGE SQL
    IMMUTABLE
    RETURNS NULL ON NULL INPUT
    RETURN a + b;

在 PL/pgSQL 中使用参数名称递增整数：

Increment an integer, making use of an argument name, in PL/pgSQL:

CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
        BEGIN
                RETURN i + 1;
        END;
$$ LANGUAGE plpgsql;

返回一个包含多个输出参数的记录：

Return a record containing multiple output parameters:

CREATE FUNCTION dup(in int, out f1 int, out f2 text)
    AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
    LANGUAGE SQL;

SELECT * FROM dup(42);

您可以使用显式命名的复合类型更详细地执行相同的操作：

You can do the same thing more verbosely with an explicitly named composite type:

CREATE TYPE dup_result AS (f1 int, f2 text);

CREATE FUNCTION dup(int) RETURNS dup_result
    AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
    LANGUAGE SQL;

SELECT * FROM dup(42);

返回多列的另一种方法是使用 TABLE 函数：

Another way to return multiple columns is to use a TABLE function:

CREATE FUNCTION dup(int) RETURNS TABLE(f1 int, f2 text)
    AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
    LANGUAGE SQL;

SELECT * FROM dup(42);

但是， TABLE 函数与前一个示例不同，因为它实际上返回记录 set ，而不仅仅是一个记录。

However, a TABLE function is different from the preceding examples, because it actually returns a set of records, not just one record.

Writing SECURITY DEFINER Functions Safely

因为 SECURITY DEFINER 函数是使用其所有者的权限执行的，所以需要小心确保无法滥用该函数。为了安全起见，应将 search_path 设置为排除任何不受信任用户可写的模式。这可以防止恶意用户创建掩盖函数打算使用的对象（例如，表、函数和运算符）的对象。在这方面特别重要的是临时表模式，它默认情况下首先被搜索，并且通常是任何人都可以写入的。可以通过强制临时模式最后被搜索来获得安全的安排。为此，请将 pg_temp 写为 search_path 中的最后一个条目。此函数说明了安全用法：

Because a SECURITY DEFINER function is executed with the privileges of the user that owns it, care is needed to ensure that the function cannot be misused. For security, search_path should be set to exclude any schemas writable by untrusted users. This prevents malicious users from creating objects (e.g., tables, functions, and operators) that mask objects intended to be used by the function. Particularly important in this regard is the temporary-table schema, which is searched first by default, and is normally writable by anyone. A secure arrangement can be obtained by forcing the temporary schema to be searched last. To do this, write pg_temp as the last entry in search_path. This function illustrates safe usage:

CREATE FUNCTION check_password(uname TEXT, pass TEXT)
RETURNS BOOLEAN AS $$
DECLARE passed BOOLEAN;
BEGIN
        SELECT  (pwd = $2) INTO passed
        FROM    pwds
        WHERE   username = $1;

        RETURN passed;
END;
$$  LANGUAGE plpgsql
    SECURITY DEFINER
    -- Set a secure search_path: trusted schema(s), then 'pg_temp'.
    SET search_path = admin, pg_temp;

此函数的目的是访问表 admin.pwds 。但如果没有 SET 子句，或 SET 子句只提到了 admin ，可以通过创建一个名为 pwds 的临时表来破坏此函数。

This function’s intention is to access a table admin.pwds. But without the SET clause, or with a SET clause mentioning only admin, the function could be subverted by creating a temporary table named pwds.

如果安全定义者函数打算创建角色，并且以非超级用户身份运行，则还应使用 SET 子句将 createrole_self_grant 设置为已知值。

If the security definer function intends to create roles, and if it is running as a non-superuser, createrole_self_grant should also be set to a known value using the SET clause.

需要牢记的另一点是，默认情况下，会向 PUBLIC 授予新创建函数的执行权限（有关更多信息，请参阅 Section 5.7 ）。您经常需要将安全定义器函数的使用限制为部分用户。为此，您必须撤消默认 PUBLIC 权限，然后选择性地授予执行权限。为了避免在所有用户均可访问新函数的时间段内创建它，并在单一事务中设置该权限。例如：

Another point to keep in mind is that by default, execute privilege is granted to PUBLIC for newly created functions (see Section 5.7 for more information). Frequently you will wish to restrict use of a security definer function to only some users. To do that, you must revoke the default PUBLIC privileges and then grant execute privilege selectively. To avoid having a window where the new function is accessible to all, create it and set the privileges within a single transaction. For example:

BEGIN;
CREATE FUNCTION check_password(uname TEXT, pass TEXT) ... SECURITY DEFINER;
REVOKE ALL ON FUNCTION check_password(uname TEXT, pass TEXT) FROM PUBLIC;
GRANT EXECUTE ON FUNCTION check_password(uname TEXT, pass TEXT) TO admins;
COMMIT;

Compatibility

SQL 标准中定义了一个 CREATE FUNCTION 命令。PostgreSQL 实现可以兼容使用，但有许多扩展。相反，SQL 标准指定了一些 PostgreSQL 中未实现的可选特性。

A CREATE FUNCTION command is defined in the SQL standard. The PostgreSQL implementation can be used in a compatible way but has many extensions. Conversely, the SQL standard specifies a number of optional features that are not implemented in PostgreSQL.

以下是一些重要的兼容性问题：

The following are important compatibility issues:

可以编写简单的 LANGUAGE SQL 函数使其既符合标准，又可移植到其他实现。使用高级特性、优化属性或其他语言的更复杂函数，在很大程度上必然是特定于 PostgreSQL 的。

Simple LANGUAGE SQL functions can be written in a way that is both standard-conforming and portable to other implementations. More complex functions using advanced features, optimization attributes, or other languages will necessarily be specific to PostgreSQL in a significant way.

See Also

ALTER FUNCTION 、 DROP FUNCTION 、 GRANT 、 LOAD 、 REVOKE

ALTER FUNCTION, DROP FUNCTION, GRANT, LOAD, REVOKE