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A PL/pgSQL Function

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Somebody wanted to know how to write a basic PostgreSQL PL/pgSQL function that returned a full name whether or not the middle name was provided. That’s pretty simple. There are principally two ways to write that type of concatenation function. One uses formal parameter names and the other uses positional values in lieu of the formal parameter names.

The two ways enjoy two techniques (SQL language and PL/pgSQL language), which gives us four possible solutions. I’ve also provided a conditional drop statement for the full_name function. If you’re new to PostgreSQL the DROP statement might make you scratch your head because you’re wondering why you need to use the formal parameter list. The DROP statement needs the parameter list because PostgeSQL lets you overload schema/database functions and procedures.

The code is for a named parameter lists using the SQL language is:

DROP FUNCTION IF EXISTS full_name
( IN pv_first_name  text
, IN pv_middle_name text
, IN pv_full_name   text);
 
CREATE FUNCTION full_name
( IN  pv_first_name  text
, IN  pv_middle_name text
, IN  pv_last_name   text
, OUT pv_full_name   text) AS
   'SELECT  pv_first_name
    ||      CASE
              WHEN pv_middle_name IS NOT NULL THEN '' '' || pv_middle_name || '' ''
              ELSE '' ''
            END
    ||      pv_last_name'
    LANGUAGE SQL;

The code is for a positional parameter lists using the SQL language is:

DROP FUNCTION IF EXISTS full_name
( IN text
, IN text
, IN text);
 
CREATE FUNCTION full_name
( IN text
, IN text
, IN text
, OUT text) AS
   'SELECT  $1
    ||      CASE
              WHEN $2 IS NOT NULL THEN '' '' || $2 || '' ''
              ELSE '' ''
            END
    ||      $3'
    LANGUAGE SQL;

You would re-write the function in the PL/pgSQL language as follows (please note the named parameter list):

CREATE FUNCTION full_name
( IN  pv_first_name   text
, IN  pv_middle_name  text
, IN  pv_last_name    text) RETURNS text AS
$$
DECLARE
  lv_output text;
BEGIN
  IF pv_middle_name IS NULL THEN
    lv_output = CONCAT(pv_first_name, N' ', pv_last_name);
  ELSE
    lv_output = CONCAT(pv_first_name, N' ', pv_middle_name, N' ', pv_first_name);
  END IF;
  RETURN lv_output;
END
$$
LANGUAGE plpgsql IMMUTABLE;

You can test either version of the program with the following two queries from the pseudo table dual, which isn’t require in the SELECT statement:

SELECT full_name('Henry',NULL,'Pym') AS "Ant-Man"
UNION ALL
SELECT full_name('Henry','''Hank''','Pym') AS "Ant-Man";

It prints:

Ant-Man
text
----------------
Henry Pym
Henry 'Hank' Pym

As always, I hope this helps those looking for how to accomplish a concatenation function in PostgreSQL.

Written by maclochlainn

January 22nd, 2015 at 1:03 am

Posted in PostgreSQL,sql

Tagged with ,

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