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Postgresql function_basics.pdf

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This document provides an overview of PostgreSQL functions including: - Functions can take various forms like SQL, procedural languages, internal, and C-language functions. - They are used for things like operators, data types, indexes, triggers, and aggregates. - Functions are created with CREATE FUNCTION and executed through normal SQL. - The document discusses function attributes, creation, varieties of languages, and provides examples of SQL functions and PL/pgSQL functions.

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Overview Function Basics By Example PostgreSQL Functions By Example Joe Conway joe.conway@credativ.com credativ Group January 20, 2012 Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages What are Functions? Full fledged SQL objects Many other database objects are implemented with them Fundamental part of PostgreSQL’s system architecture Created with CREATE FUNCTION Executed through normal SQL target-list: SELECT myfunc(f1) FROM foo; FROM clause: SELECT * FROM myfunc(); WHERE clause: SELECT * FROM foo WHERE myfunc(f1) = 42; Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages How are they Used? Functions Operators Data types Index methods Casts Triggers Aggregates Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages What Forms Can They Take? PostgreSQL provides four kinds of functions: SQL Procedural Languages Internal C-language Arguments Base, composite, or combinations Scalar or array Pseudo or polymorphic VARIADIC IN/OUT/INOUT Return Singleton or set (SETOF) Base or composite type Pseudo or polymorphic http://www.postgresql.org/docs/9.1/interactive/sql-createfunction.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages SQL Functions Behavior Executes an arbitrary list of SQL statements separated by semicolons Last statement may be INSERT, UPDATE, or DELETE with RETURNING clause Arguments Referenced by function body using $n: $1 is first arg, etc. . . If composite type, then dot notation $1.name used to access Only used as data values, not as identifiers Return If singleton, first row of last query result returned, NULL on no result If SETOF, all rows of last query result returned, empty set on no result http://www.postgresql.org/docs/9.1/interactive/xfunc-sql.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages Procedural Languages User-defined functions Written in languages besides SQL and C Task is passed to a special handler that knows the details of the language Handler could be self-contained (e.g. PL/pgSQL) Handler could be dynamically loaded (e.g. PL/Perl) http://www.postgresql.org/docs/9.1/interactive/xplang.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages Internal Functions Statically linked C functions Could use CREATE FUNCTION to create additional alias names for an internal function Most internal functions expect to be declared STRICT CREATE FUNCTION square_root(double precision) RETURNS double precision AS ’dsqrt’ LANGUAGE internal STRICT; http://www.postgresql.org/docs/9.1/interactive/xfunc-internal.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages C Language Functions User-defined functions written in C Compiled into dynamically loadable objects (also called shared libraries) Loaded by the server on demand contrib is good source of examples Same as internal function coding conventions Require PG MODULE MAGIC call Needs separate topic http://www.postgresql.org/docs/9.1/interactive/xfunc-c.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Introduction Uses Varieties Languages Language Availability PostgreSQL includes the following server-side procedural languages: http://www.postgresql.org/docs/9.1/interactive/xplang.html PL/pgSQL Perl Python Tcl Other languages available: http://pgfoundry.org/softwaremap/trove_list.php?form_cat=311 Java PHP Ruby R Shell others . . . Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Creation Attributes Creating New Functions CREATE [ OR REPLACE ] FUNCTION name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } defexpr ] [, ... [ RETURNS rettype | RETURNS TABLE ( colname coltype [, ...] ) ] { LANGUAGE langname | WINDOW | IMMUTABLE | STABLE | VOLATILE | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER | COST execution_cost | ROWS result_rows | SET configuration_parameter { TO value | = value | FROM CURRENT } | AS ’definition’ | AS ’obj_file’, ’link_symbol’ } ... [ WITH ( attribute [, ...] ) ] http://www.postgresql.org/docs/9.1/interactive/sql-createfunction.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Creation Attributes Dollar Quoting Works for all character strings Particularly useful for function bodies CREATE OR REPLACE FUNCTION dummy () RETURNS text AS $Q$ DECLARE result text; BEGIN PERFORM ’SELECT 1+1’; RETURN ’ok’; END; $Q$ LANGUAGE plpgsql; http://www.postgresql.org/docs/9.1/static/sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Creation Attributes Function Overloading IN argument signature used Avoid ambiguities: Type (e.g. REAL vs. DOUBLE PRECISION) Function name same as IN composite field name VARIADIC vs same type scalar CREATE OR REPLACE FUNCTION foo (text) RETURNS text AS $$ SELECT $1 $$ LANGUAGE sql; CREATE OR REPLACE FUNCTION foo (int) RETURNS text AS $$ SELECT ($1 + 1)::text $$ LANGUAGE sql; SELECT foo(’42’), foo(41); foo | foo -----+----- 42 | 42 (1 row) http://www.postgresql.org/docs/9.1/interactive/xfunc-overload.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Creation Attributes Changing Existing Functions Once created, dependent objects may be created Must do DROP FUNCTION ... CASCADE to recreate Or use OR REPLACE to avoid dropping dependent objects Very useful for large dependency tree Can’t be used in some circumstances (must drop/recreate instead). You cannot: change function name or argument types change return type change types of any OUT parameters CREATE OR REPLACE FUNCTION ...; Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Creation Attributes Volatility VOLATILE (default) Each call can return a different result Example: random() or timeofday() Functions modifying table contents must be declared volatile STABLE Returns same result for same arguments within single query Example: now() Consider configuration settings that affect output IMMUTABLE Always returns the same result for the same arguments Example: lower(’ABC’) Unaffected by configuration settings Not dependent on table contents select lower(’ABC’), now(), timeofday() from generate_series(1,3); Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Creation Attributes Behavior with Null Input Values CALLED ON NULL INPUT (default) Function called normally with the null input values RETURNS NULL ON NULL INPUT Function not called when null input values are present Instead, null is returned automatically CREATE FUNCTION sum1 (int, int) RETURNS int AS $$ SELECT $1 + $2 $$ LANGUAGE SQL RETURNS NULL ON NULL INPUT; CREATE FUNCTION sum2 (int, int) RETURNS int AS $$ SELECT COALESCE($1, 0) + COALESCE($2, 0) $$ LANGUAGE SQL CALLED ON NULL INPUT; SELECT sum1(9, NULL) IS NULL AS "true", sum2(9, NULL); true | sum2 ------+------ t | 9 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example Creation Attributes Security Attributes SECURITY INVOKER (default) Function executed with the rights of the current user SECURITY DEFINER Executed with rights of creator, like ”setuid” CREATE TABLE foo (f1 int); REVOKE ALL ON foo FROM public; CREATE FUNCTION see_foo() RETURNS SETOF foo AS $$ SELECT * FROM foo $$ LANGUAGE SQL SECURITY DEFINER; c - guest You are now connected to database "postgres" as user "guest". SELECT * FROM foo; ERROR: permission denied for relation foo SELECT * FROM see_foo(); f1 ---- (0 rows) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Simple CREATE FUNCTION sum (text, text) RETURNS text AS $$ SELECT $1 || ’ ’ || $2 $$ LANGUAGE SQL; SELECT sum(’hello’, ’world’); sum ------------- hello world (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Custom Operator CREATE OPERATOR + ( procedure = sum, leftarg = text, rightarg = text ); SELECT ’hello’ + ’world’; ?column? ------------- hello world (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Custom Aggregate CREATE OR REPLACE FUNCTION concat_ws_comma(text, ANYELEMENT) RETURNS text AS $$ SELECT concat_ws(’,’, $1, $2) $$ LANGUAGE sql; CREATE AGGREGATE str_agg (ANYELEMENT) ( sfunc = concat_ws_comma, stype = text); SELECT str_agg(f1) FROM foo; str_agg --------- 41,42 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions SETOF with OUT Arguments CREATE OR REPLACE FUNCTION sql_with_rows(OUT a int, OUT b text) RETURNS SETOF RECORD AS $$ values (1,’a’),(2,’b’) $$ LANGUAGE SQL; select * from sql_with_rows(); a | b ---+--- 1 | a 2 | b (2 rows) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions INSERT RETURNING CREATE TABLE foo (f0 serial, f1 int, f2 text); CREATE OR REPLACE FUNCTION sql_insert_returning(INOUT f1 int, INOUT f2 text, OUT id int) AS $$ INSERT INTO foo(f1, f2) VALUES ($1,$2) RETURNING f1, f2, f0 $$ LANGUAGE SQL; SELECT * FROM sql_insert_returning(1,’a’); f1 | f2 | id ----+----+---- 1 | a | 1 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Composite Argument CREATE TABLE emp (name text, salary numeric, age integer, cubicle point); CREATE FUNCTION double_salary(emp) RETURNS numeric AS $$ SELECT $1.salary * 2 AS salary; $$ LANGUAGE SQL; SELECT name, double_salary(emp.*) AS dream FROM emp WHERE emp.cubicle ~= point ’(2,1)’; SELECT name, double_salary(ROW(name, salary*1.1, age, cubicle)) AS dream FROM emp; Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Polymorphic CREATE FUNCTION myappend(anyarray, anyelement) RETURNS anyarray AS $$ SELECT $1 || $2; $$ LANGUAGE SQL; SELECT myappend(ARRAY[42,6], 21), myappend(ARRAY[’abc’,’def’], ’xyz’); myappend | myappend -----------+--------------- {42,6,21} | {abc,def,xyz} (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Target List versus FROM Clause CREATE FUNCTION new_emp() RETURNS emp AS $$ SELECT ROW(’None’, 1000.0, 25, ’(2,2)’)::emp; $$ LANGUAGE SQL; SELECT new_emp(); new_emp -------------------------- (None,1000.0,25,"(2,2)") SELECT * FROM new_emp(); name | salary | age | cubicle ------+--------+-----+--------- None | 1000.0 | 25 | (2,2) SELECT (new_emp()).name; name ------ None Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions VARIADIC CREATE FUNCTION mleast(VARIADIC numeric[]) RETURNS numeric AS $$ SELECT min($1[i]) FROM generate_subscripts($1, 1) g(i); $$ LANGUAGE SQL; SELECT mleast(10, -1, 5, 4.4); mleast -------- -1 (1 row) SELECT mleast(42, 6, 42.42); mleast -------- 6 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions DEFAULT Arguments CREATE FUNCTION foo(a int, b int DEFAULT 2, c int DEFAULT 3) RETURNS int LANGUAGE SQL AS $$SELECT $1 + $2 + $3$$; SELECT foo(10, 20, 30); foo ----- 60 (1 row) SELECT foo(10, 20); foo ----- 33 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions PL/pgSQL PL/pgSQL is SQL plus procedural elements variables if/then/else loops cursors error checking Loading the language handler into a database: createlang plpgsql dbname http://www.postgresql.org/docs/9.1/interactive/plpgsql.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Simple CREATE OR REPLACE FUNCTION sum (text, text) RETURNS text AS $$ BEGIN RETURN $1 || ’ ’ || $2; END; $$ LANGUAGE plpgsql; SELECT sum(’hello’, ’world’); sum ------------- hello world (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Parameter ALIAS CREATE OR REPLACE FUNCTION sum (int, int) RETURNS int AS $$ DECLARE i ALIAS FOR $1; j ALIAS FOR $2; sum int; BEGIN sum := i + j; RETURN sum; END; $$ LANGUAGE plpgsql; SELECT sum(41, 1); sum ----- 42 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Named Parameters CREATE OR REPLACE FUNCTION sum (i int, j int) RETURNS int AS $$ DECLARE sum int; BEGIN sum := i + j; RETURN sum; END; $$ LANGUAGE plpgsql; SELECT sum(41, 1); sum ----- 42 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Control Structures: IF ... CREATE OR REPLACE FUNCTION even (i int) RETURNS boolean AS $$ DECLARE tmp int; BEGIN tmp := i % 2; IF tmp = 0 THEN RETURN true; ELSE RETURN false; END IF; END; $$ LANGUAGE plpgsql; SELECT even(3), even(42); even | even ------+------ f | t (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Control Structures: FOR ... LOOP CREATE OR REPLACE FUNCTION factorial (i numeric) RETURNS numeric AS $$ DECLARE tmp numeric; result numeric; BEGIN result := 1; FOR tmp IN 1 .. i LOOP result := result * tmp; END LOOP; RETURN result; END; $$ LANGUAGE plpgsql; SELECT factorial(42::numeric); factorial ------------------------------------------------------ 1405006117752879898543142606244511569936384000000000 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Control Structures: WHILE ... LOOP CREATE OR REPLACE FUNCTION factorial (i numeric) RETURNS numeric AS $$ DECLARE tmp numeric; result numeric; BEGIN result := 1; tmp := 1; WHILE tmp <= i LOOP result := result * tmp; tmp := tmp + 1; END LOOP; RETURN result; END; $$ LANGUAGE plpgsql; SELECT factorial(42::numeric); factorial ------------------------------------------------------ 1405006117752879898543142606244511569936384000000000 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Recursive CREATE OR REPLACE FUNCTION factorial (i numeric) RETURNS numeric AS $$ BEGIN IF i = 0 THEN RETURN 1; ELSIF i = 1 THEN RETURN 1; ELSE RETURN i * factorial(i - 1); END IF; END; $$ LANGUAGE plpgsql; SELECT factorial(42::numeric); factorial ------------------------------------------------------ 1405006117752879898543142606244511569936384000000000 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Record types CREATE OR REPLACE FUNCTION format () RETURNS text AS $$ DECLARE tmp RECORD; BEGIN SELECT INTO tmp 1 + 1 AS a, 2 + 2 AS b; RETURN ’a = ’ || tmp.a || ’; b = ’ || tmp.b; END; $$ LANGUAGE plpgsql; select format(); format -------------- a = 2; b = 4 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions PERFORM CREATE OR REPLACE FUNCTION func_w_side_fx() RETURNS void AS $$ INSERT INTO foo VALUES (41),(42) $$ LANGUAGE sql; CREATE OR REPLACE FUNCTION dummy () RETURNS text AS $$ BEGIN PERFORM func_w_side_fx(); RETURN ’OK’; END; $$ LANGUAGE plpgsql; SELECT dummy(); SELECT * FROM foo; f1 ---- 41 42 (2 rows) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Dynamic SQL CREATE OR REPLACE FUNCTION get_foo(i int) RETURNS foo AS $$ DECLARE rec RECORD; BEGIN EXECUTE ’SELECT * FROM foo WHERE f1 = ’ || i INTO rec; RETURN rec; END; $$ LANGUAGE plpgsql; SELECT * FROM get_foo(42); f1 ---- 42 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Cursors CREATE OR REPLACE FUNCTION totalbalance() RETURNS numeric AS $$ DECLARE tmp RECORD; result numeric; BEGIN result := 0.00; FOR tmp IN SELECT * FROM foo LOOP result := result + tmp.f1; END LOOP; RETURN result; END; $$ LANGUAGE plpgsql; SELECT totalbalance(); totalbalance -------------- 83.00 (1 row) Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Error Handling CREATE OR REPLACE FUNCTION safe_add(a integer, b integer) RETURNS integer AS $$ BEGIN RETURN a + b; EXCEPTION WHEN numeric_value_out_of_range THEN -- do some important stuff RETURN -1; WHEN OTHERS THEN -- do some other important stuff RETURN -1; END; $$ LANGUAGE plpgsql; http://www.postgresql.org/docs/9.1/interactive/errcodes-appendix.html Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Nested Exception Blocks CREATE FUNCTION merge_db(key integer, data text) RETURNS void AS $$ BEGIN LOOP UPDATE db SET b = data WHERE a = key; IF found THEN RETURN; END IF; BEGIN INSERT INTO db (a, b) VALUES (key, data); RETURN; EXCEPTION WHEN unique_violation THEN -- do nothing END; END LOOP; EXCEPTION WHEN OTHERS THEN -- do something else END; $$ LANGUAGE plpgsql; Joe Conway SCALE10X-PGDay
Overview Function Basics By Example SQL Functions PL/pgSQL Functions Thank You Questions? Joe Conway SCALE10X-PGDay

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Postgresql function_basics.pdf

  • 1. Overview Function Basics By Example PostgreSQL Functions By Example Joe Conway [email protected] credativ Group January 20, 2012 Joe Conway SCALE10X-PGDay
  • 2. Overview Function Basics By Example Introduction Uses Varieties Languages What are Functions? Full fledged SQL objects Many other database objects are implemented with them Fundamental part of PostgreSQL’s system architecture Created with CREATE FUNCTION Executed through normal SQL target-list: SELECT myfunc(f1) FROM foo; FROM clause: SELECT * FROM myfunc(); WHERE clause: SELECT * FROM foo WHERE myfunc(f1) = 42; Joe Conway SCALE10X-PGDay
  • 3. Overview Function Basics By Example Introduction Uses Varieties Languages How are they Used? Functions Operators Data types Index methods Casts Triggers Aggregates Joe Conway SCALE10X-PGDay
  • 4. Overview Function Basics By Example Introduction Uses Varieties Languages What Forms Can They Take? PostgreSQL provides four kinds of functions: SQL Procedural Languages Internal C-language Arguments Base, composite, or combinations Scalar or array Pseudo or polymorphic VARIADIC IN/OUT/INOUT Return Singleton or set (SETOF) Base or composite type Pseudo or polymorphic http://www.postgresql.org/docs/9.1/interactive/sql-createfunction.html Joe Conway SCALE10X-PGDay
  • 5. Overview Function Basics By Example Introduction Uses Varieties Languages SQL Functions Behavior Executes an arbitrary list of SQL statements separated by semicolons Last statement may be INSERT, UPDATE, or DELETE with RETURNING clause Arguments Referenced by function body using $n: $1 is first arg, etc. . . If composite type, then dot notation $1.name used to access Only used as data values, not as identifiers Return If singleton, first row of last query result returned, NULL on no result If SETOF, all rows of last query result returned, empty set on no result http://www.postgresql.org/docs/9.1/interactive/xfunc-sql.html Joe Conway SCALE10X-PGDay
  • 6. Overview Function Basics By Example Introduction Uses Varieties Languages Procedural Languages User-defined functions Written in languages besides SQL and C Task is passed to a special handler that knows the details of the language Handler could be self-contained (e.g. PL/pgSQL) Handler could be dynamically loaded (e.g. PL/Perl) http://www.postgresql.org/docs/9.1/interactive/xplang.html Joe Conway SCALE10X-PGDay
  • 7. Overview Function Basics By Example Introduction Uses Varieties Languages Internal Functions Statically linked C functions Could use CREATE FUNCTION to create additional alias names for an internal function Most internal functions expect to be declared STRICT CREATE FUNCTION square_root(double precision) RETURNS double precision AS ’dsqrt’ LANGUAGE internal STRICT; http://www.postgresql.org/docs/9.1/interactive/xfunc-internal.html Joe Conway SCALE10X-PGDay
  • 8. Overview Function Basics By Example Introduction Uses Varieties Languages C Language Functions User-defined functions written in C Compiled into dynamically loadable objects (also called shared libraries) Loaded by the server on demand contrib is good source of examples Same as internal function coding conventions Require PG MODULE MAGIC call Needs separate topic http://www.postgresql.org/docs/9.1/interactive/xfunc-c.html Joe Conway SCALE10X-PGDay
  • 9. Overview Function Basics By Example Introduction Uses Varieties Languages Language Availability PostgreSQL includes the following server-side procedural languages: http://www.postgresql.org/docs/9.1/interactive/xplang.html PL/pgSQL Perl Python Tcl Other languages available: http://pgfoundry.org/softwaremap/trove_list.php?form_cat=311 Java PHP Ruby R Shell others . . . Joe Conway SCALE10X-PGDay
  • 10. Overview Function Basics By Example Creation Attributes Creating New Functions CREATE [ OR REPLACE ] FUNCTION name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } defexpr ] [, ... [ RETURNS rettype | RETURNS TABLE ( colname coltype [, ...] ) ] { LANGUAGE langname | WINDOW | IMMUTABLE | STABLE | VOLATILE | CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER | COST execution_cost | ROWS result_rows | SET configuration_parameter { TO value | = value | FROM CURRENT } | AS ’definition’ | AS ’obj_file’, ’link_symbol’ } ... [ WITH ( attribute [, ...] ) ] http://www.postgresql.org/docs/9.1/interactive/sql-createfunction.html Joe Conway SCALE10X-PGDay
  • 11. Overview Function Basics By Example Creation Attributes Dollar Quoting Works for all character strings Particularly useful for function bodies CREATE OR REPLACE FUNCTION dummy () RETURNS text AS $Q$ DECLARE result text; BEGIN PERFORM ’SELECT 1+1’; RETURN ’ok’; END; $Q$ LANGUAGE plpgsql; http://www.postgresql.org/docs/9.1/static/sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING Joe Conway SCALE10X-PGDay
  • 12. Overview Function Basics By Example Creation Attributes Function Overloading IN argument signature used Avoid ambiguities: Type (e.g. REAL vs. DOUBLE PRECISION) Function name same as IN composite field name VARIADIC vs same type scalar CREATE OR REPLACE FUNCTION foo (text) RETURNS text AS $$ SELECT $1 $$ LANGUAGE sql; CREATE OR REPLACE FUNCTION foo (int) RETURNS text AS $$ SELECT ($1 + 1)::text $$ LANGUAGE sql; SELECT foo(’42’), foo(41); foo | foo -----+----- 42 | 42 (1 row) http://www.postgresql.org/docs/9.1/interactive/xfunc-overload.html Joe Conway SCALE10X-PGDay
  • 13. Overview Function Basics By Example Creation Attributes Changing Existing Functions Once created, dependent objects may be created Must do DROP FUNCTION ... CASCADE to recreate Or use OR REPLACE to avoid dropping dependent objects Very useful for large dependency tree Can’t be used in some circumstances (must drop/recreate instead). You cannot: change function name or argument types change return type change types of any OUT parameters CREATE OR REPLACE FUNCTION ...; Joe Conway SCALE10X-PGDay
  • 14. Overview Function Basics By Example Creation Attributes Volatility VOLATILE (default) Each call can return a different result Example: random() or timeofday() Functions modifying table contents must be declared volatile STABLE Returns same result for same arguments within single query Example: now() Consider configuration settings that affect output IMMUTABLE Always returns the same result for the same arguments Example: lower(’ABC’) Unaffected by configuration settings Not dependent on table contents select lower(’ABC’), now(), timeofday() from generate_series(1,3); Joe Conway SCALE10X-PGDay
  • 15. Overview Function Basics By Example Creation Attributes Behavior with Null Input Values CALLED ON NULL INPUT (default) Function called normally with the null input values RETURNS NULL ON NULL INPUT Function not called when null input values are present Instead, null is returned automatically CREATE FUNCTION sum1 (int, int) RETURNS int AS $$ SELECT $1 + $2 $$ LANGUAGE SQL RETURNS NULL ON NULL INPUT; CREATE FUNCTION sum2 (int, int) RETURNS int AS $$ SELECT COALESCE($1, 0) + COALESCE($2, 0) $$ LANGUAGE SQL CALLED ON NULL INPUT; SELECT sum1(9, NULL) IS NULL AS "true", sum2(9, NULL); true | sum2 ------+------ t | 9 (1 row) Joe Conway SCALE10X-PGDay
  • 16. Overview Function Basics By Example Creation Attributes Security Attributes SECURITY INVOKER (default) Function executed with the rights of the current user SECURITY DEFINER Executed with rights of creator, like ”setuid” CREATE TABLE foo (f1 int); REVOKE ALL ON foo FROM public; CREATE FUNCTION see_foo() RETURNS SETOF foo AS $$ SELECT * FROM foo $$ LANGUAGE SQL SECURITY DEFINER; c - guest You are now connected to database "postgres" as user "guest". SELECT * FROM foo; ERROR: permission denied for relation foo SELECT * FROM see_foo(); f1 ---- (0 rows) Joe Conway SCALE10X-PGDay
  • 17. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Simple CREATE FUNCTION sum (text, text) RETURNS text AS $$ SELECT $1 || ’ ’ || $2 $$ LANGUAGE SQL; SELECT sum(’hello’, ’world’); sum ------------- hello world (1 row) Joe Conway SCALE10X-PGDay
  • 18. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Custom Operator CREATE OPERATOR + ( procedure = sum, leftarg = text, rightarg = text ); SELECT ’hello’ + ’world’; ?column? ------------- hello world (1 row) Joe Conway SCALE10X-PGDay
  • 19. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Custom Aggregate CREATE OR REPLACE FUNCTION concat_ws_comma(text, ANYELEMENT) RETURNS text AS $$ SELECT concat_ws(’,’, $1, $2) $$ LANGUAGE sql; CREATE AGGREGATE str_agg (ANYELEMENT) ( sfunc = concat_ws_comma, stype = text); SELECT str_agg(f1) FROM foo; str_agg --------- 41,42 (1 row) Joe Conway SCALE10X-PGDay
  • 20. Overview Function Basics By Example SQL Functions PL/pgSQL Functions SETOF with OUT Arguments CREATE OR REPLACE FUNCTION sql_with_rows(OUT a int, OUT b text) RETURNS SETOF RECORD AS $$ values (1,’a’),(2,’b’) $$ LANGUAGE SQL; select * from sql_with_rows(); a | b ---+--- 1 | a 2 | b (2 rows) Joe Conway SCALE10X-PGDay
  • 21. Overview Function Basics By Example SQL Functions PL/pgSQL Functions INSERT RETURNING CREATE TABLE foo (f0 serial, f1 int, f2 text); CREATE OR REPLACE FUNCTION sql_insert_returning(INOUT f1 int, INOUT f2 text, OUT id int) AS $$ INSERT INTO foo(f1, f2) VALUES ($1,$2) RETURNING f1, f2, f0 $$ LANGUAGE SQL; SELECT * FROM sql_insert_returning(1,’a’); f1 | f2 | id ----+----+---- 1 | a | 1 (1 row) Joe Conway SCALE10X-PGDay
  • 22. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Composite Argument CREATE TABLE emp (name text, salary numeric, age integer, cubicle point); CREATE FUNCTION double_salary(emp) RETURNS numeric AS $$ SELECT $1.salary * 2 AS salary; $$ LANGUAGE SQL; SELECT name, double_salary(emp.*) AS dream FROM emp WHERE emp.cubicle ~= point ’(2,1)’; SELECT name, double_salary(ROW(name, salary*1.1, age, cubicle)) AS dream FROM emp; Joe Conway SCALE10X-PGDay
  • 23. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Polymorphic CREATE FUNCTION myappend(anyarray, anyelement) RETURNS anyarray AS $$ SELECT $1 || $2; $$ LANGUAGE SQL; SELECT myappend(ARRAY[42,6], 21), myappend(ARRAY[’abc’,’def’], ’xyz’); myappend | myappend -----------+--------------- {42,6,21} | {abc,def,xyz} (1 row) Joe Conway SCALE10X-PGDay
  • 24. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Target List versus FROM Clause CREATE FUNCTION new_emp() RETURNS emp AS $$ SELECT ROW(’None’, 1000.0, 25, ’(2,2)’)::emp; $$ LANGUAGE SQL; SELECT new_emp(); new_emp -------------------------- (None,1000.0,25,"(2,2)") SELECT * FROM new_emp(); name | salary | age | cubicle ------+--------+-----+--------- None | 1000.0 | 25 | (2,2) SELECT (new_emp()).name; name ------ None Joe Conway SCALE10X-PGDay
  • 25. Overview Function Basics By Example SQL Functions PL/pgSQL Functions VARIADIC CREATE FUNCTION mleast(VARIADIC numeric[]) RETURNS numeric AS $$ SELECT min($1[i]) FROM generate_subscripts($1, 1) g(i); $$ LANGUAGE SQL; SELECT mleast(10, -1, 5, 4.4); mleast -------- -1 (1 row) SELECT mleast(42, 6, 42.42); mleast -------- 6 (1 row) Joe Conway SCALE10X-PGDay
  • 26. Overview Function Basics By Example SQL Functions PL/pgSQL Functions DEFAULT Arguments CREATE FUNCTION foo(a int, b int DEFAULT 2, c int DEFAULT 3) RETURNS int LANGUAGE SQL AS $$SELECT $1 + $2 + $3$$; SELECT foo(10, 20, 30); foo ----- 60 (1 row) SELECT foo(10, 20); foo ----- 33 (1 row) Joe Conway SCALE10X-PGDay
  • 27. Overview Function Basics By Example SQL Functions PL/pgSQL Functions PL/pgSQL PL/pgSQL is SQL plus procedural elements variables if/then/else loops cursors error checking Loading the language handler into a database: createlang plpgsql dbname http://www.postgresql.org/docs/9.1/interactive/plpgsql.html Joe Conway SCALE10X-PGDay
  • 28. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Simple CREATE OR REPLACE FUNCTION sum (text, text) RETURNS text AS $$ BEGIN RETURN $1 || ’ ’ || $2; END; $$ LANGUAGE plpgsql; SELECT sum(’hello’, ’world’); sum ------------- hello world (1 row) Joe Conway SCALE10X-PGDay
  • 29. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Parameter ALIAS CREATE OR REPLACE FUNCTION sum (int, int) RETURNS int AS $$ DECLARE i ALIAS FOR $1; j ALIAS FOR $2; sum int; BEGIN sum := i + j; RETURN sum; END; $$ LANGUAGE plpgsql; SELECT sum(41, 1); sum ----- 42 (1 row) Joe Conway SCALE10X-PGDay
  • 30. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Named Parameters CREATE OR REPLACE FUNCTION sum (i int, j int) RETURNS int AS $$ DECLARE sum int; BEGIN sum := i + j; RETURN sum; END; $$ LANGUAGE plpgsql; SELECT sum(41, 1); sum ----- 42 (1 row) Joe Conway SCALE10X-PGDay
  • 31. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Control Structures: IF ... CREATE OR REPLACE FUNCTION even (i int) RETURNS boolean AS $$ DECLARE tmp int; BEGIN tmp := i % 2; IF tmp = 0 THEN RETURN true; ELSE RETURN false; END IF; END; $$ LANGUAGE plpgsql; SELECT even(3), even(42); even | even ------+------ f | t (1 row) Joe Conway SCALE10X-PGDay
  • 32. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Control Structures: FOR ... LOOP CREATE OR REPLACE FUNCTION factorial (i numeric) RETURNS numeric AS $$ DECLARE tmp numeric; result numeric; BEGIN result := 1; FOR tmp IN 1 .. i LOOP result := result * tmp; END LOOP; RETURN result; END; $$ LANGUAGE plpgsql; SELECT factorial(42::numeric); factorial ------------------------------------------------------ 1405006117752879898543142606244511569936384000000000 (1 row) Joe Conway SCALE10X-PGDay
  • 33. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Control Structures: WHILE ... LOOP CREATE OR REPLACE FUNCTION factorial (i numeric) RETURNS numeric AS $$ DECLARE tmp numeric; result numeric; BEGIN result := 1; tmp := 1; WHILE tmp <= i LOOP result := result * tmp; tmp := tmp + 1; END LOOP; RETURN result; END; $$ LANGUAGE plpgsql; SELECT factorial(42::numeric); factorial ------------------------------------------------------ 1405006117752879898543142606244511569936384000000000 (1 row) Joe Conway SCALE10X-PGDay
  • 34. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Recursive CREATE OR REPLACE FUNCTION factorial (i numeric) RETURNS numeric AS $$ BEGIN IF i = 0 THEN RETURN 1; ELSIF i = 1 THEN RETURN 1; ELSE RETURN i * factorial(i - 1); END IF; END; $$ LANGUAGE plpgsql; SELECT factorial(42::numeric); factorial ------------------------------------------------------ 1405006117752879898543142606244511569936384000000000 (1 row) Joe Conway SCALE10X-PGDay
  • 35. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Record types CREATE OR REPLACE FUNCTION format () RETURNS text AS $$ DECLARE tmp RECORD; BEGIN SELECT INTO tmp 1 + 1 AS a, 2 + 2 AS b; RETURN ’a = ’ || tmp.a || ’; b = ’ || tmp.b; END; $$ LANGUAGE plpgsql; select format(); format -------------- a = 2; b = 4 (1 row) Joe Conway SCALE10X-PGDay
  • 36. Overview Function Basics By Example SQL Functions PL/pgSQL Functions PERFORM CREATE OR REPLACE FUNCTION func_w_side_fx() RETURNS void AS $$ INSERT INTO foo VALUES (41),(42) $$ LANGUAGE sql; CREATE OR REPLACE FUNCTION dummy () RETURNS text AS $$ BEGIN PERFORM func_w_side_fx(); RETURN ’OK’; END; $$ LANGUAGE plpgsql; SELECT dummy(); SELECT * FROM foo; f1 ---- 41 42 (2 rows) Joe Conway SCALE10X-PGDay
  • 37. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Dynamic SQL CREATE OR REPLACE FUNCTION get_foo(i int) RETURNS foo AS $$ DECLARE rec RECORD; BEGIN EXECUTE ’SELECT * FROM foo WHERE f1 = ’ || i INTO rec; RETURN rec; END; $$ LANGUAGE plpgsql; SELECT * FROM get_foo(42); f1 ---- 42 (1 row) Joe Conway SCALE10X-PGDay
  • 38. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Cursors CREATE OR REPLACE FUNCTION totalbalance() RETURNS numeric AS $$ DECLARE tmp RECORD; result numeric; BEGIN result := 0.00; FOR tmp IN SELECT * FROM foo LOOP result := result + tmp.f1; END LOOP; RETURN result; END; $$ LANGUAGE plpgsql; SELECT totalbalance(); totalbalance -------------- 83.00 (1 row) Joe Conway SCALE10X-PGDay
  • 39. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Error Handling CREATE OR REPLACE FUNCTION safe_add(a integer, b integer) RETURNS integer AS $$ BEGIN RETURN a + b; EXCEPTION WHEN numeric_value_out_of_range THEN -- do some important stuff RETURN -1; WHEN OTHERS THEN -- do some other important stuff RETURN -1; END; $$ LANGUAGE plpgsql; http://www.postgresql.org/docs/9.1/interactive/errcodes-appendix.html Joe Conway SCALE10X-PGDay
  • 40. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Nested Exception Blocks CREATE FUNCTION merge_db(key integer, data text) RETURNS void AS $$ BEGIN LOOP UPDATE db SET b = data WHERE a = key; IF found THEN RETURN; END IF; BEGIN INSERT INTO db (a, b) VALUES (key, data); RETURN; EXCEPTION WHEN unique_violation THEN -- do nothing END; END LOOP; EXCEPTION WHEN OTHERS THEN -- do something else END; $$ LANGUAGE plpgsql; Joe Conway SCALE10X-PGDay
  • 41. Overview Function Basics By Example SQL Functions PL/pgSQL Functions Thank You Questions? Joe Conway SCALE10X-PGDay