PostgreSQL - Functions

 PostgreSQL functions, also known as Stored Procedures, allow you to carry out operations that would normally take several queries and round trips in a single function within the database. Functions allow database reuse as other applications can interact directly with your stored procedures instead of a middle-tier or duplicating code.

Functions can be created in a language of your choice like SQL, PL/pgSQL, C, Python, etc.

Syntax

The basic syntax to create a function is as follows −

CREATE [OR REPLACE] FUNCTION function_name (arguments) 
RETURNS return_datatype AS $variable_name$
   DECLARE
      declaration;
      [...]
   BEGIN
      < function_body >
      [...]
      RETURN { variable_name | value }
   END; LANGUAGE plpgsql;

Where,

• function-name specifies the name of the function.
• [OR REPLACE] option allows modifying an existing function.
• The function must contain a return statement.
• RETURN clause specifies that data type you are going to return from the function. The return_datatype can be a base, composite, or domain type, or can reference the type of a table column.
• function-body contains the executable part.
• The AS keyword is used for creating a standalone function.
• plpgsql is the name of the language that the function is implemented in. Here, we use this option for PostgreSQL, it Can be SQL, C, internal, or the name of a user-defined procedural language. For backward compatibility, the name can be enclosed by single quotes.

Example

The following example illustrates creating and calling a standalone function. This function returns the total number of records in the COMPANY table. We will use the COMPANY table, which has the following records −

testdb# select * from COMPANY;
 id | name  | age | address   | salary
----+-------+-----+-----------+--------
  1 | Paul  |  32 | California|  20000
  2 | Allen |  25 | Texas     |  15000
  3 | Teddy |  23 | Norway    |  20000
  4 | Mark  |  25 | Rich-Mond |  65000
  5 | David |  27 | Texas     |  85000
  6 | Kim   |  22 | South-Hall|  45000
  7 | James |  24 | Houston   |  10000
(7 rows)

Function totalRecords() is as follows −

CREATE OR REPLACE FUNCTION totalRecords ()
RETURNS integer AS $total$
declare
	total integer;
BEGIN
   SELECT count(*) into total FROM COMPANY;
   RETURN total;
END;
$total$ LANGUAGE plpgsql;

When the above query is executed, the result would be −

testdb# CREATE FUNCTION

Now, let us execute a call to this function and check the records in the COMPANY table

testdb=# select totalRecords();

When the above query is executed, the result would be −

 totalrecords
--------------
      7
(1 row)