Example: stock market

PostgreSQL Functions By Example - joeconway.com

OverviewFunction BasicsBy ExamplePostgreSQL Functions By ExampleJoe GroupJanuary 20, 2012 Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sWhat are Functions ?Full fledged SQL objectsMany other database objects are implemented with themFundamental part of PostgreSQL s system architectureCreated withCREATE FUNCTIONE xecuted through normal SQLtarget-list:SELECT myfunc(f1) FROM foo;FROM clause:SELECT * FROM myfunc();WHERE clause:SELECT * FROM foo WHERE myfunc(f1) = 42;Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sHow are they Used?FunctionsOperatorsData typesIndex methodsCastsTriggersAggregatesJoe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sWhat Forms Can They Take? PostgreSQL provides four kinds of Functions :SQLP rocedural LanguagesInternalC-languageArgumentsBase , composite, or combinationsScalar or arrayPseudo or polymorphicVARIADICIN/OUT/INOUTR eturnSingleton or set (SETOF)Base or composite typePseudo or ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sSQL FunctionsBehaviorExecutes an arbitrary list of SQL statements separated bysemicolonsLast statement may be INSERT, UPDATE, or DELETE withRETURNING clauseArgumentsReferenced by function body using $n: $1 is first arg, etc.

Overview Function Basics By Example Introduction Uses Varieties Languages What are Functions? Full edged SQL objects Many other database objects are implemented with them

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Transcription of PostgreSQL Functions By Example - joeconway.com

1 OverviewFunction BasicsBy ExamplePostgreSQL Functions By ExampleJoe GroupJanuary 20, 2012 Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sWhat are Functions ?Full fledged SQL objectsMany other database objects are implemented with themFundamental part of PostgreSQL s system architectureCreated withCREATE FUNCTIONE xecuted through normal SQLtarget-list:SELECT myfunc(f1) FROM foo;FROM clause:SELECT * FROM myfunc();WHERE clause:SELECT * FROM foo WHERE myfunc(f1) = 42;Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sHow are they Used?FunctionsOperatorsData typesIndex methodsCastsTriggersAggregatesJoe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sWhat Forms Can They Take? PostgreSQL provides four kinds of Functions :SQLP rocedural LanguagesInternalC-languageArgumentsBase , composite, or combinationsScalar or arrayPseudo or polymorphicVARIADICIN/OUT/INOUTR eturnSingleton or set (SETOF)Base or composite typePseudo or ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sSQL FunctionsBehaviorExecutes an arbitrary list of SQL statements separated bysemicolonsLast statement may be INSERT, UPDATE, or DELETE withRETURNING clauseArgumentsReferenced by function body using $n: $1 is first arg, etc.

2 If composite type, then dot notation $ used to accessOnly used as data values, not as identifiersReturnIf singleton, first row of last query result returned, NULL on noresultIf SETOF, all rows of last query result returned, empty set onno ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sProcedural LanguagesUser-defined functionsWritten in languages besides SQL and CTask is passed to a special handler that knows the details ofthe languageHandler could be self-contained ( PL/pgSQL)Handler could be dynamically loaded ( PL/Perl) ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sInternal FunctionsStatically linked C functionsCould use CREATE FUNCTION to create additional aliasnames for an internal functionMost internal Functions expect to be declared STRICTCREATE FUNCTION square_root(double precision)RETURNS double precision AS dsqrt LANGUAGE internal STRICT; ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sC Language FunctionsUser-defined Functions written in CCompiled into dynamically loadable objects (also called sharedlibraries)Loaded by the server on demandcontrib is good source of examplesSame as internal function coding conventionsRequire PGMODULEMAGIC callNeeds separate ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleIntroductionUsesVarietiesLanguage sLanguage AvailabilityPostgreSQL includes the following server-side procedurallanguages: languages available.

3 Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleCreationAttributesCreating New FunctionsCREATE [ 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 [, ..] ) ] ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleCreationAttributesDollar QuotingWorks for all character stringsParticularly useful for function bodiesCREATE OR REPLACE FUNCTION dummy () RETURNS text AS$Q$DECLARE result text;BEGINPERFORM SELECT 1+1 ;RETURN ok ;END;$Q$LANGUAGE plpgsql; #SQL-SYNTAX-DOLLAR-QUOTINGJoe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleCreationAttributesFunction OverloadingIN argument signature usedAvoid ambiguities:Type ( REAL vs.)

4 DOUBLE PRECISION)Function name same as IN composite field nameVARIADIC vs same type scalarCREATE 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) ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleCreationAttributesChanging Existing FunctionsOnce created, dependent objects may be createdMust doDROP FUNCTION .. CASCADEto recreateOr useOR REPLACEto avoid dropping dependent objectsVery useful for large dependency treeCan t be used in some circumstances (must drop/recreateinstead). You cannot:change function name or argument typeschange return typechange types of any OUT parametersCREATE OR REPLACE FUNCTION ..;Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleCreationAttributesVolatilityVOLAT ILE (default)Each call can return a different resultExample:random()ortimeofday()Funct ions modifying table contents must be declared volatileSTABLER eturns same result for same arguments within single queryExample:now()Consider configuration settings that affect outputIMMUTABLEA lways returns the same result for the same argumentsExample:lower( ABC )Unaffected by configuration settingsNot dependent on table contentsselect lower( ABC ), now(), timeofday() from generate_series(1,3).

5 Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleCreationAttributesBehavior with Null Input ValuesCALLED ON NULL INPUT (default)Function called normally with the null input valuesRETURNS NULL ON NULL INPUTF unction not called when null input values are presentInstead, null is returned automaticallyCREATE 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 ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleCreationAttributesSecurity AttributesSECURITY INVOKER (default)Function executed with the rights of the current userSECURITY DEFINERE xecuted 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 - guestYou are now connected to database "postgres" as user "guest".

6 SELECT * FROM foo;ERROR: permission denied for relation fooSELECT * FROM see_foo();f1----(0 rows)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsSimpleCREATE FUNCTION sum (text, text)RETURNS text AS $$SELECT $1 || || $2$$ LANGUAGE SQL;SELECT sum( hello , world );sum-------------hello world(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsCustom OperatorCREATE OPERATOR + (procedure = sum,leftarg = text,rightarg = text);SELECT hello + world ;?column?-------------hello world(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsCustom AggregateCREATE 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 ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsSETOF with OUT ArgumentsCREATE 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 | a2 | b(2 rows)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsINSERT RETURNINGCREATE TABLE foo (f0 serial, f1 int, f2 text).

7 CREATE OR REPLACE FUNCTIONsql_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 ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsComposite ArgumentCREATE TABLE emp (name text,salary numeric,age integer,cubicle point);CREATE FUNCTION double_salary(emp) RETURNS numeric AS $$SELECT $ * 2 AS salary;$$ LANGUAGE SQL;SELECT name, double_salary(emp.*) AS dreamFROM emp WHERE ~= point (2,1) ;SELECT name,double_salary(ROW(name, salary* , age, cubicle)) AS dreamFROM emp;Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsPolymorphicCREATE 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 ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsTarget List versus FROM ClauseCREATE FUNCTION new_emp() RETURNS emp AS $$SELECT ROW( None , , 25, (2,2) )::emp;$$ LANGUAGE SQL;SELECT new_emp();new_emp----------------------- ---(None, ,25,"(2,2)")SELECT * FROM new_emp();name | salary | age | cubicle------+--------+-----+---------No ne | | 25 | (2,2)SELECT (new_emp()).

8 Name;name------NoneJoe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsVARIADICCREATE 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, );mleast---------1(1 row)SELECT mleast(42, 6, );mleast--------6(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsDEFAULT ArgumentsCREATE 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 ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsPL/pgSQLPL/pgSQL is SQL plus procedural elementsvariablesif/then/elseloopscursor serror checkingLoading the language handler into a database:createlang plpgsql ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsSimpleCREATE OR REPLACE FUNCTION sum (text, text)RETURNS text AS $$BEGINRETURN $1 || || $2;END;$$ LANGUAGE plpgsql;SELECT sum( hello , world );sum-------------hello world(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsParameter ALIASCREATE OR REPLACE FUNCTION sum (int, int)RETURNS int AS $$DECLAREi ALIAS FOR $1;j ALIAS FOR $2;sum int;BEGINsum := i + j;RETURN sum;END;$$ LANGUAGE plpgsql;SELECT sum(41, 1).

9 Sum-----42(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsNamed ParametersCREATE OR REPLACE FUNCTION sum (i int, j int)RETURNS int AS $$DECLAREsum int;BEGINsum := i + j;RETURN sum;END;$$ LANGUAGE plpgsql;SELECT sum(41, 1);sum-----42(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsControl Structures: IF ..CREATE OR REPLACE FUNCTION even (i int)RETURNS boolean AS $$DECLAREtmp int;BEGINtmp := i % 2;IF tmp = 0 THEN RETURN true;ELSE RETURN false;END IF;END;$$ LANGUAGE plpgsql;SELECT even(3), even(42);even | even------+------f | t(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsControl Structures: FOR .. LOOPCREATE OR REPLACE FUNCTION factorial (i numeric)RETURNS numeric AS $$DECLAREtmp numeric; result numeric;BEGIN result := 1;FOR tmp IN 1 .. i LOOP result := result * tmp;END LOOP;RETURN result;END;$$ LANGUAGE plpgsql;SELECT factorial(42::numeric);factorial-------- ---------------------------------------- ------1405006117752879898543142606244511 569936384000000000(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsControl Structures: WHILE.

10 LOOPCREATE 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-------- ---------------------------------------- ------1405006117752879898543142606244511 569936384000000000(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsRecursiveCREATE OR REPLACE FUNCTION factorial (i numeric)RETURNS numeric AS $$BEGINIF i = 0 THENRETURN 1;ELSIF i = 1 THENRETURN 1;ELSERETURN i * factorial(i - 1);END IF;END;$$ LANGUAGE plpgsql;SELECT factorial(42::numeric);factorial-------- ---------------------------------------- ------1405006117752879898543142606244511 569936384000000000(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsRecord typesCREATE OR REPLACE FUNCTION format ()RETURNS text AS $$DECLAREtmp RECORD;BEGINSELECT INTO tmp 1 + 1 AS a, 2 + 2 AS b;RETURN a = || || ; b = || ;END;$$ LANGUAGE plpgsql;select format();format--------------a = 2; b = 4(1 row)Joe ConwaySCALE10X-PGDayOverviewFunction BasicsBy ExampleSQL FunctionsPL/pgSQL FunctionsPERFORMCREATE 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 $$BEGINPERFORM func_w_side_fx();RETURN OK ;END;$$ LANGUAGE plpgsql;SELECT dummy();SELECT * FROM foo.


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