write a function in postgresql code example

Example 1: create function in postgresql

create [or replace] function function_name(param_list)
   returns return_type 
   language plpgsql
as $$
declare 
-- variable declaration
begin
 -- logic
end;
$$

Example 2: plpgsql create function

CREATE FUNCTION function_name(argument1 type,argument2 type)
 RETURNS type AS
BEGIN
  staments;
END;
LANGUAGE 'language_name';

Example 3: plpgsql create function

postgres=# Create or replace function fun1(n int) returns int 

as

$$

Begin

Insert into test values (n,'2019-11-26');

Return 1;

End;

$$

Language 'plpgsql';

CREATE FUNCTION

postgres=#

Example 4: postgresql functions

CASE
     WHEN condition_1  THEN result_1
     WHEN condition_2  THEN result_2
     ...
     ELSE  result_n
END