1CREATE FUNCTION(7) PostgreSQL 15.4 Documentation CREATE FUNCTION(7)
2
6 CREATE_FUNCTION - define a new function
7
9 CREATE [ OR REPLACE ] FUNCTION
10 name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } default_expr ] [, ...] ] )
11 [ RETURNS rettype
12 | RETURNS TABLE ( column_name column_type [, ...] ) ]
13 { LANGUAGE lang_name
14 | TRANSFORM { FOR TYPE type_name } [, ... ]
15 | WINDOW
16 | { IMMUTABLE | STABLE | VOLATILE }
17 | [ NOT ] LEAKPROOF
18 | { CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT }
19 | { [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER }
20 | PARALLEL { UNSAFE | RESTRICTED | SAFE }
21 | COST execution_cost
22 | ROWS result_rows
23 | SUPPORT support_function
24 | SET configuration_parameter { TO value | = value | FROM CURRENT }
25 | AS 'definition'
26 | AS 'obj_file', 'link_symbol'
27 | sql_body
28 } ...
29
31 CREATE FUNCTION defines a new function. CREATE OR REPLACE FUNCTION
32 will either create a new function, or replace an existing definition.
33 To be able to define a function, the user must have the USAGE privilege
34 on the language.
35 If a schema name is included, then the function is created in the
37 specified schema. Otherwise it is created in the current schema. The
38 name of the new function must not match any existing function or
39 procedure with the same input argument types in the same schema.
40 However, functions and procedures of different argument types can share
41 a name (this is called overloading).
42 To replace the current definition of an existing function, use CREATE
44 OR REPLACE FUNCTION. It is not possible to change the name or argument
45 types of a function this way (if you tried, you would actually be
46 creating a new, distinct function). Also, CREATE OR REPLACE FUNCTION
47 will not let you change the return type of an existing function. To do
48 that, you must drop and recreate the function. (When using OUT
49 parameters, that means you cannot change the types of any OUT
50 parameters except by dropping the function.)
51 When CREATE OR REPLACE FUNCTION is used to replace an existing
53 function, the ownership and permissions of the function do not change.
54 All other function properties are assigned the values specified or
55 implied in the command. You must own the function to replace it (this
56 includes being a member of the owning role).
57 If you drop and then recreate a function, the new function is not the
59 same entity as the old; you will have to drop existing rules, views,
60 triggers, etc. that refer to the old function. Use CREATE OR REPLACE
61 FUNCTION to change a function definition without breaking objects that
62 refer to the function. Also, ALTER FUNCTION can be used to change most
63 of the auxiliary properties of an existing function.
64 The user that creates the function becomes the owner of the function.
66 To be able to create a function, you must have USAGE privilege on the
68 argument types and the return type.
69 Refer to Section 38.3 for further information on writing functions.
71
73 name
74 The name (optionally schema-qualified) of the function to create.
75 argmode
77 The mode of an argument: IN, OUT, INOUT, or VARIADIC. If omitted,
78 the default is IN. Only OUT arguments can follow a VARIADIC one.
79 Also, OUT and INOUT arguments cannot be used together with the
80 RETURNS TABLE notation.
81 argname
83 The name of an argument. Some languages (including SQL and
84 PL/pgSQL) let you use the name in the function body. For other
85 languages the name of an input argument is just extra
86 documentation, so far as the function itself is concerned; but you
87 can use input argument names when calling a function to improve
88 readability (see Section 4.3). In any case, the name of an output
89 argument is significant, because it defines the column name in the
90 result row type. (If you omit the name for an output argument, the
91 system will choose a default column name.)
92 argtype
94 The data type(s) of the function's arguments (optionally
95 schema-qualified), if any. The argument types can be base,
96 composite, or domain types, or can reference the type of a table
97 column.
98 Depending on the implementation language it might also be allowed
100 to specify “pseudo-types” such as cstring. Pseudo-types indicate
101 that the actual argument type is either incompletely specified, or
102 outside the set of ordinary SQL data types.
103 The type of a column is referenced by writing
105 table_name.column_name%TYPE. Using this feature can sometimes help
106 make a function independent of changes to the definition of a
107 table.
108 default_expr
110 An expression to be used as default value if the parameter is not
111 specified. The expression has to be coercible to the argument type
112 of the parameter. Only input (including INOUT) parameters can have
113 a default value. All input parameters following a parameter with a
114 default value must have default values as well.
115 rettype
117 The return data type (optionally schema-qualified). The return type
118 can be a base, composite, or domain type, or can reference the type
119 of a table column. Depending on the implementation language it
120 might also be allowed to specify “pseudo-types” such as cstring. If
121 the function is not supposed to return a value, specify void as the
122 return type.
123 When there are OUT or INOUT parameters, the RETURNS clause can be
125 omitted. If present, it must agree with the result type implied by
126 the output parameters: RECORD if there are multiple output
127 parameters, or the same type as the single output parameter.
128 The SETOF modifier indicates that the function will return a set of
130 items, rather than a single item.
131 The type of a column is referenced by writing
133 table_name.column_name%TYPE.
134 column_name
136 The name of an output column in the RETURNS TABLE syntax. This is
137 effectively another way of declaring a named OUT parameter, except
138 that RETURNS TABLE also implies RETURNS SETOF.
139 column_type
141 The data type of an output column in the RETURNS TABLE syntax.
142 lang_name
144 The name of the language that the function is implemented in. It
145 can be sql, c, internal, or the name of a user-defined procedural
146 language, e.g., plpgsql. The default is sql if sql_body is
147 specified. Enclosing the name in single quotes is deprecated and
148 requires matching case.
149 TRANSFORM { FOR TYPE type_name } [, ... ] }
151 Lists which transforms a call to the function should apply.
152 Transforms convert between SQL types and language-specific data
153 types; see CREATE TRANSFORM (CREATE_TRANSFORM(7)). Procedural
154 language implementations usually have hardcoded knowledge of the
155 built-in types, so those don't need to be listed here. If a
156 procedural language implementation does not know how to handle a
157 type and no transform is supplied, it will fall back to a default
158 behavior for converting data types, but this depends on the
159 implementation.
160 WINDOW
162 WINDOW indicates that the function is a window function rather than
163 a plain function. This is currently only useful for functions
164 written in C. The WINDOW attribute cannot be changed when replacing
165 an existing function definition.
166 IMMUTABLE
168 STABLE
169 VOLATILE
170 These attributes inform the query optimizer about the behavior of
171 the function. At most one choice can be specified. If none of these
172 appear, VOLATILE is the default assumption.
173 IMMUTABLE indicates that the function cannot modify the database
175 and always returns the same result when given the same argument
176 values; that is, it does not do database lookups or otherwise use
177 information not directly present in its argument list. If this
178 option is given, any call of the function with all-constant
179 arguments can be immediately replaced with the function value.
180 STABLE indicates that the function cannot modify the database, and
182 that within a single table scan it will consistently return the
183 same result for the same argument values, but that its result could
184 change across SQL statements. This is the appropriate selection for
185 functions whose results depend on database lookups, parameter
186 variables (such as the current time zone), etc. (It is
187 inappropriate for AFTER triggers that wish to query rows modified
188 by the current command.) Also note that the current_timestamp
189 family of functions qualify as stable, since their values do not
190 change within a transaction.
191 VOLATILE indicates that the function value can change even within a
193 single table scan, so no optimizations can be made. Relatively few
194 database functions are volatile in this sense; some examples are
195 random(), currval(), timeofday(). But note that any function that
196 has side-effects must be classified volatile, even if its result is
197 quite predictable, to prevent calls from being optimized away; an
198 example is setval().
199 For additional details see Section 38.7.
201 LEAKPROOF
203 LEAKPROOF indicates that the function has no side effects. It
204 reveals no information about its arguments other than by its return
205 value. For example, a function which throws an error message for
206 some argument values but not others, or which includes the argument
207 values in any error message, is not leakproof. This affects how the
208 system executes queries against views created with the
209 security_barrier option or tables with row level security enabled.
210 The system will enforce conditions from security policies and
211 security barrier views before any user-supplied conditions from the
212 query itself that contain non-leakproof functions, in order to
213 prevent the inadvertent exposure of data. Functions and operators
214 marked as leakproof are assumed to be trustworthy, and may be
215 executed before conditions from security policies and security
216 barrier views. In addition, functions which do not take arguments
217 or which are not passed any arguments from the security barrier
218 view or table do not have to be marked as leakproof to be executed
219 before security conditions. See CREATE VIEW (CREATE_VIEW(7)) and
220 Section 41.5. This option can only be set by the superuser.
221 CALLED ON NULL INPUT
223 RETURNS NULL ON NULL INPUT
224 STRICT
225 CALLED ON NULL INPUT (the default) indicates that the function will
226 be called normally when some of its arguments are null. It is then
227 the function author's responsibility to check for null values if
228 necessary and respond appropriately.
229 RETURNS NULL ON NULL INPUT or STRICT indicates that the function
231 always returns null whenever any of its arguments are null. If this
232 parameter is specified, the function is not executed when there are
233 null arguments; instead a null result is assumed automatically.
234 [EXTERNAL] SECURITY INVOKER
236 [EXTERNAL] SECURITY DEFINER
237 SECURITY INVOKER indicates that the function is to be executed with
238 the privileges of the user that calls it. That is the default.
239 SECURITY DEFINER specifies that the function is to be executed with
240 the privileges of the user that owns it.
241 The key word EXTERNAL is allowed for SQL conformance, but it is
243 optional since, unlike in SQL, this feature applies to all
244 functions not only external ones.
245 PARALLEL
247 PARALLEL UNSAFE indicates that the function can't be executed in
248 parallel mode and the presence of such a function in an SQL
249 statement forces a serial execution plan. This is the default.
250 PARALLEL RESTRICTED indicates that the function can be executed in
251 parallel mode, but the execution is restricted to parallel group
252 leader. PARALLEL SAFE indicates that the function is safe to run
253 in parallel mode without restriction.
254 Functions should be labeled parallel unsafe if they modify any
256 database state, or if they make changes to the transaction such as
257 using sub-transactions, or if they access sequences or attempt to
258 make persistent changes to settings (e.g., setval). They should be
259 labeled as parallel restricted if they access temporary tables,
260 client connection state, cursors, prepared statements, or
261 miscellaneous backend-local state which the system cannot
262 synchronize in parallel mode (e.g., setseed cannot be executed
263 other than by the group leader because a change made by another
264 process would not be reflected in the leader). In general, if a
265 function is labeled as being safe when it is restricted or unsafe,
266 or if it is labeled as being restricted when it is in fact unsafe,
267 it may throw errors or produce wrong answers when used in a
268 parallel query. C-language functions could in theory exhibit
269 totally undefined behavior if mislabeled, since there is no way for
270 the system to protect itself against arbitrary C code, but in most
271 likely cases the result will be no worse than for any other
272 function. If in doubt, functions should be labeled as UNSAFE, which
273 is the default.
274 COST execution_cost
276 A positive number giving the estimated execution cost for the
277 function, in units of cpu_operator_cost. If the function returns a
278 set, this is the cost per returned row. If the cost is not
279 specified, 1 unit is assumed for C-language and internal functions,
280 and 100 units for functions in all other languages. Larger values
281 cause the planner to try to avoid evaluating the function more
282 often than necessary.
283 ROWS result_rows
285 A positive number giving the estimated number of rows that the
286 planner should expect the function to return. This is only allowed
287 when the function is declared to return a set. The default
288 assumption is 1000 rows.
289 SUPPORT support_function
291 The name (optionally schema-qualified) of a planner support
292 function to use for this function. See Section 38.11 for details.
293 You must be superuser to use this option.
294 configuration_parameter
296 value
297 The SET clause causes the specified configuration parameter to be
298 set to the specified value when the function is entered, and then
299 restored to its prior value when the function exits. SET FROM
300 CURRENT saves the value of the parameter that is current when
301 CREATE FUNCTION is executed as the value to be applied when the
302 function is entered.
303 If a SET clause is attached to a function, then the effects of a
305 SET LOCAL command executed inside the function for the same
306 variable are restricted to the function: the configuration
307 parameter's prior value is still restored at function exit.
308 However, an ordinary SET command (without LOCAL) overrides the SET
309 clause, much as it would do for a previous SET LOCAL command: the
310 effects of such a command will persist after function exit, unless
311 the current transaction is rolled back.
312 See SET(7) and Chapter 20 for more information about allowed
314 parameter names and values.
315 definition
317 A string constant defining the function; the meaning depends on the
318 language. It can be an internal function name, the path to an
319 object file, an SQL command, or text in a procedural language.
320 It is often helpful to use dollar quoting (see Section 4.1.2.4) to
322 write the function definition string, rather than the normal single
323 quote syntax. Without dollar quoting, any single quotes or
324 backslashes in the function definition must be escaped by doubling
325 them.
326 obj_file, link_symbol
328 This form of the AS clause is used for dynamically loadable C
329 language functions when the function name in the C language source
330 code is not the same as the name of the SQL function. The string
331 obj_file is the name of the shared library file containing the
332 compiled C function, and is interpreted as for the LOAD command.
333 The string link_symbol is the function's link symbol, that is, the
334 name of the function in the C language source code. If the link
335 symbol is omitted, it is assumed to be the same as the name of the
336 SQL function being defined. The C names of all functions must be
337 different, so you must give overloaded C functions different C
338 names (for example, use the argument types as part of the C names).
339 When repeated CREATE FUNCTION calls refer to the same object file,
341 the file is only loaded once per session. To unload and reload the
342 file (perhaps during development), start a new session.
343 sql_body
345 The body of a LANGUAGE SQL function. This can either be a single
346 statement
347 RETURN expression
349 or a block
351 BEGIN ATOMIC
353 statement;
354 statement;
355 ...
356 statement;
357 END
358 This is similar to writing the text of the function body as a
360 string constant (see definition above), but there are some
361 differences: This form only works for LANGUAGE SQL, the string
362 constant form works for all languages. This form is parsed at
363 function definition time, the string constant form is parsed at
364 execution time; therefore this form cannot support polymorphic
365 argument types and other constructs that are not resolvable at
366 function definition time. This form tracks dependencies between the
367 function and objects used in the function body, so DROP ... CASCADE
368 will work correctly, whereas the form using string literals may
369 leave dangling functions. Finally, this form is more compatible
370 with the SQL standard and other SQL implementations.
371
373 PostgreSQL allows function overloading; that is, the same name can be
374 used for several different functions so long as they have distinct
375 input argument types. Whether or not you use it, this capability
376 entails security precautions when calling functions in databases where
377 some users mistrust other users; see Section 10.3.
378 Two functions are considered the same if they have the same names and
380 input argument types, ignoring any OUT parameters. Thus for example
381 these declarations conflict:
382 CREATE FUNCTION foo(int) ...
384 CREATE FUNCTION foo(int, out text) ...
385 Functions that have different argument type lists will not be
387 considered to conflict at creation time, but if defaults are provided
388 they might conflict in use. For example, consider
389 CREATE FUNCTION foo(int) ...
391 CREATE FUNCTION foo(int, int default 42) ...
392 A call foo(10) will fail due to the ambiguity about which function
394 should be called.
395
397 The full SQL type syntax is allowed for declaring a function's
398 arguments and return value. However, parenthesized type modifiers
399 (e.g., the precision field for type numeric) are discarded by CREATE
400 FUNCTION. Thus for example CREATE FUNCTION foo (varchar(10)) ... is
401 exactly the same as CREATE FUNCTION foo (varchar) ....
402 When replacing an existing function with CREATE OR REPLACE FUNCTION,
404 there are restrictions on changing parameter names. You cannot change
405 the name already assigned to any input parameter (although you can add
406 names to parameters that had none before). If there is more than one
407 output parameter, you cannot change the names of the output parameters,
408 because that would change the column names of the anonymous composite
409 type that describes the function's result. These restrictions are made
410 to ensure that existing calls of the function do not stop working when
411 it is replaced.
412 If a function is declared STRICT with a VARIADIC argument, the
414 strictness check tests that the variadic array as a whole is non-null.
415 The function will still be called if the array has null elements.
416
418 Add two integers using an SQL function:
419 CREATE FUNCTION add(integer, integer) RETURNS integer
421 AS 'select $1 + $2;'
422 LANGUAGE SQL
423 IMMUTABLE
424 RETURNS NULL ON NULL INPUT;
425 The same function written in a more SQL-conforming style, using
427 argument names and an unquoted body:
428 CREATE FUNCTION add(a integer, b integer) RETURNS integer
430 LANGUAGE SQL
431 IMMUTABLE
432 RETURNS NULL ON NULL INPUT
433 RETURN a + b;
434 Increment an integer, making use of an argument name, in PL/pgSQL:
436 CREATE OR REPLACE FUNCTION increment(i integer) RETURNS integer AS $$
438 BEGIN
439 RETURN i + 1;
440 END;
441 $$ LANGUAGE plpgsql;
442 Return a record containing multiple output parameters:
444 CREATE FUNCTION dup(in int, out f1 int, out f2 text)
446 AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
447 LANGUAGE SQL;
448 SELECT * FROM dup(42);
450 You can do the same thing more verbosely with an explicitly named
452 composite type:
453 CREATE TYPE dup_result AS (f1 int, f2 text);
455 CREATE FUNCTION dup(int) RETURNS dup_result
457 AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
458 LANGUAGE SQL;
459 SELECT * FROM dup(42);
461 Another way to return multiple columns is to use a TABLE function:
463 CREATE FUNCTION dup(int) RETURNS TABLE(f1 int, f2 text)
465 AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
466 LANGUAGE SQL;
467 SELECT * FROM dup(42);
469 However, a TABLE function is different from the preceding examples,
471 because it actually returns a set of records, not just one record.
472
474 Because a SECURITY DEFINER function is executed with the privileges of
475 the user that owns it, care is needed to ensure that the function
476 cannot be misused. For security, search_path should be set to exclude
477 any schemas writable by untrusted users. This prevents malicious users
478 from creating objects (e.g., tables, functions, and operators) that
479 mask objects intended to be used by the function. Particularly
480 important in this regard is the temporary-table schema, which is
481 searched first by default, and is normally writable by anyone. A secure
482 arrangement can be obtained by forcing the temporary schema to be
483 searched last. To do this, write pg_temp as the last entry in
484 search_path. This function illustrates safe usage:
485 CREATE FUNCTION check_password(uname TEXT, pass TEXT)
487 RETURNS BOOLEAN AS $$
488 DECLARE passed BOOLEAN;
489 BEGIN
490 SELECT (pwd = $2) INTO passed
491 FROM pwds
492 WHERE username = $1;
493 RETURN passed;
495 END;
496 $$ LANGUAGE plpgsql
497 SECURITY DEFINER
498 -- Set a secure search_path: trusted schema(s), then 'pg_temp'.
499 SET search_path = admin, pg_temp;
500 This function's intention is to access a table admin.pwds. But without
502 the SET clause, or with a SET clause mentioning only admin, the
503 function could be subverted by creating a temporary table named pwds.
504 Before PostgreSQL version 8.3, the SET clause was not available, and so
506 older functions may contain rather complicated logic to save, set, and
507 restore search_path. The SET clause is far easier to use for this
508 purpose.
509 Another point to keep in mind is that by default, execute privilege is
511 granted to PUBLIC for newly created functions (see Section 5.7 for more
512 information). Frequently you will wish to restrict use of a security
513 definer function to only some users. To do that, you must revoke the
514 default PUBLIC privileges and then grant execute privilege selectively.
515 To avoid having a window where the new function is accessible to all,
516 create it and set the privileges within a single transaction. For
517 example:
518 BEGIN;
520 CREATE FUNCTION check_password(uname TEXT, pass TEXT) ... SECURITY DEFINER;
521 REVOKE ALL ON FUNCTION check_password(uname TEXT, pass TEXT) FROM PUBLIC;
522 GRANT EXECUTE ON FUNCTION check_password(uname TEXT, pass TEXT) TO admins;
523 COMMIT;
524
526 A CREATE FUNCTION command is defined in the SQL standard. The
527 PostgreSQL implementation can be used in a compatible way but has many
528 extensions. Conversely, the SQL standard specifies a number of optional
529 features that are not implemented in PostgreSQL.
530 The following are important compatibility issues:
532 • OR REPLACE is a PostgreSQL extension.
534 • For compatibility with some other database systems, argmode can be
536 written either before or after argname. But only the first way is
537 standard-compliant.
538 • For parameter defaults, the SQL standard specifies only the syntax
540 with the DEFAULT key word. The syntax with = is used in T-SQL and
541 Firebird.
542 • The SETOF modifier is a PostgreSQL extension.
544 • Only SQL is standardized as a language.
546 • All other attributes except CALLED ON NULL INPUT and RETURNS NULL
548 ON NULL INPUT are not standardized.
549 • For the body of LANGUAGE SQL functions, the SQL standard only
551 specifies the sql_body form.
552 Simple LANGUAGE SQL functions can be written in a way that is both
554 standard-conforming and portable to other implementations. More complex
555 functions using advanced features, optimization attributes, or other
556 languages will necessarily be specific to PostgreSQL in a significant
557 way.
558
560 ALTER FUNCTION (ALTER_FUNCTION(7)), DROP FUNCTION (DROP_FUNCTION(7)),
561 GRANT(7), LOAD(7), REVOKE(7)
562PostgreSQL 15.4 2023 CREATE FUNCTION(7)