159 lines
4.4 KiB
Plaintext
159 lines
4.4 KiB
Plaintext
---------------------------------------------------------------------------
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--
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-- funcs.sql-
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-- Tutorial on using functions in POSTGRES.
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--
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--
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-- Copyright (c) 1994-5, Regents of the University of California
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--
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-- $Id: funcs.source,v 1.1.1.1 1996/07/09 06:22:34 scrappy Exp $
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--
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---------------------------------------------------------------------------
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-----------------------------
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-- Creating SQL Functions on Base Types
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-- a CREATE FUNCTION statement lets you create a new function that
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-- can be used in expressions (in SELECT, INSERT, etc.). We will start
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-- with functions that return values of base types.
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-----------------------------
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--
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-- let's create a simple SQL function that takes no arguments and
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-- returns 1
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CREATE FUNCTION one() RETURNS int4
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AS 'SELECT 1 as ONE' LANGUAGE 'sql';
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--
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-- functions can be used in any expressions (eg. in the target list or
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-- qualifications)
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SELECT one() AS answer;
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--
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-- here's how you create a function that takes arguments. The following
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-- function returns the sum of its two arguments:
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CREATE FUNCTION add_em(int4, int4) RETURNS int4
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AS 'SELECT $1 + $2' LANGUAGE 'sql';
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SELECT add_em(1, 2) AS answer;
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-----------------------------
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-- Creating SQL Functions on Composite Types
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-- it is also possible to create functions that return values of
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-- composite types.
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-----------------------------
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-- before we create more sophisticated functions, let's populate an EMP
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-- table
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CREATE TABLE EMP (
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name text,
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salary int4,
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age int4,
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dept char16
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);
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INSERT INTO EMP VALUES ('Sam', 1200, 16, 'toy')
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INSERT INTO EMP VALUES ('Claire', 5000, 32, 'shoe')
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INSERT INTO EMP VALUES ('Andy', -1000, 2, 'candy')
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INSERT INTO EMP VALUES ('Bill', 4200, 36, 'shoe')
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INSERT INTO EMP VALUES ('Ginger', 4800, 30, 'candy');
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-- the argument of a function can also be a tuple. For instance,
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-- double_salary takes a tuple of the EMP table
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CREATE FUNCTION double_salary(EMP) RETURNS int4
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AS 'SELECT $1.salary * 2 AS salary' LANGUAGE 'sql';
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SELECT name, double_salary(EMP) AS dream
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FROM EMP
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WHERE EMP.dept = 'toy';
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-- the return value of a function can also be a tuple. However, make sure
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-- that the expressions in the target list is in the same order as the
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-- columns of EMP.
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CREATE FUNCTION new_emp() RETURNS EMP
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AS 'SELECT \'None\'::text AS name,
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1000 AS salary,
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25 AS age,
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\'none\'::char16 AS dept'
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LANGUAGE 'sql';
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-- you can then project a column out of resulting the tuple by using the
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-- "function notation" for projection columns. (ie. bar(foo) is equivalent
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-- to foo.bar) Note that we don't support new_emp().name at this moment.
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SELECT name(new_emp()) AS nobody;
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-- let's try one more function that returns tuples
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CREATE FUNCTION high_pay() RETURNS setof EMP
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AS 'SELECT * FROM EMP where salary > 1500'
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LANGUAGE 'sql';
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SELECT name(high_pay()) AS overpaid;
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-----------------------------
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-- Creating SQL Functions with multiple SQL statements
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-- you can also create functions that do more than just a SELECT.
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-----------------------------
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-- you may have noticed that Andy has a negative salary. We'll create a
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-- function that removes employees with negative salaries.
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SELECT * FROM EMP;
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CREATE FUNCTION clean_EMP () RETURNS int4
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AS 'DELETE FROM EMP WHERE EMP.salary <= 0
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SELECT 1 AS ignore_this'
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LANGUAGE 'sql';
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SELECT clean_EMP();
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SELECT * FROM EMP;
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-----------------------------
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-- Creating C Functions
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-- in addition to SQL functions, you can also create C functions.
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-- See C-code/funcs.c for the definition of the C functions.
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-----------------------------
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CREATE FUNCTION add_one(int4) RETURNS int4
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AS '_OBJWD_/funcs.so' LANGUAGE 'c';
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CREATE FUNCTION concat16(char16, char16) RETURNS char16
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AS '_OBJWD_/funcs.so' LANGUAGE 'c';
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CREATE FUNCTION copytext(text) RETURNS text
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AS '_OBJWD_/funcs.so' LANGUAGE 'c';
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CREATE FUNCTION c_overpaid(EMP, int4) RETURNS bool
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AS '_OBJWD_/funcs.so' LANGUAGE 'c';
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SELECT add_one(3) AS four;
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SELECT concat16('abc', 'xyz') AS newchar16;
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SELECT copytext('hello world!');
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SELECT name, c_overpaid(EMP, 1500) AS overpaid
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FROM EMP
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WHERE name = 'Bill' or name = 'Sam';
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-- remove functions that were created in this file
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DROP FUNCTION c_overpaid(EMP, int4)
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DROP FUNCTION copytext(text)
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DROP FUNCTION concat16(char16,char16)
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DROP FUNCTION add_one(int4)
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DROP FUNCTION clean_EMP()
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DROP FUNCTION new_emp()
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DROP FUNCTION add_em(int4, int4)
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DROP FUNCTION one();
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DROP TABLE EMP;
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