PostgreSQL/Postgre SQL/Declare Variable

Using variable declaration options

postgres=# -- Using variable declaration options
postgres=#
postgres=# CREATE FUNCTION example_function () RETURNS text AS "
postgres"#   DECLARE
postgres"#
postgres"#     -- Declare a constant integer with a default value of 5.
postgres"#     five CONSTANT INTEGER := 5;
postgres"#
postgres"#     -- Declare an integer with a default value of 100 that cannot be NULL.
postgres"#     ten INTEGER NOT NULL := 10;
postgres"#
postgres"#     -- Declare a character with a default value of "a".
postgres"#     letter CHAR DEFAULT ""a"";
postgres"#
postgres"#   BEGIN
postgres"#   return letter;
postgres"#   END;
postgres"# " LANGUAGE "plpgsql";
CREATE FUNCTION
postgres=#
postgres=# select example_function ();
 example_function
------------------
 a
(1 row)
postgres=#
postgres=# drop function example_function ();
DROP FUNCTION
postgres=#
postgres=#

Variable Declarations

postgres=# -- Variable Declarations
postgres=#
postgres=# CREATE FUNCTION identifier () RETURNS int4 AS "
postgres"#   DECLARE
postgres"#
postgres"#      -- Declare an integer.
postgres"#     subject_id INTEGER;
postgres"#
postgres"#      -- Declare a variable length character.
postgres"#     book_title VARCHAR(10);
postgres"#
postgres"#       -- Declare a floating point number.
postgres"#     book_price FLOAT;
postgres"#
postgres"#   BEGIN
postgres"#     return 10;
postgres"#   END;
postgres"# " LANGUAGE "plpgsql";
ERROR:  function "identifier" already exists with same argument types
postgres=#
postgres=# select identifier();
 identifier
------------
         10
(1 row)
postgres=#
postgres=# drop function identifier();
DROP FUNCTION
postgres=#
postgres=#