Question

I have a table being created in a PostgreSQL ( version 9 ) database by a third party product and I need to change that table to add a new column then set the column in question to a standard value.

I have the following in my function:

CREATE FUNCTION alterscorecolumns()
  RETURNS void AS
$BODY$

ALTER TABLE "hi_scores" ADD "total_score" integer;

UPDATE "hi_scores" SET total_score = score1+score2+score3;

$BODY$

However, I’m not allowed to do this because it doesn’t know that the total_score field exists. I just get the message ERROR: column "total_score" of relation "hi_scores" does not exist.

I am guessing there is some execution-plan related reason for this and that maybe I need to tell it to run the ALTER TABLE before it tries to perform the update, but I can’t seem to figure out what I need to do.

Answer 1

You can’t do it that way. The SQL in the function is parsed when you create the function. At the time of the creation of the function the column is not there, so you get the error message.

You will need to use dynamic SQL to run the UPDATE statement.

Something like:

CREATE FUNCTION alterscorecolumns()
  RETURNS void AS
$BODY$
begin
  execute 'ALTER TABLE hi_scores ADD total_score integer';
  execute 'UPDATE hi_scores SET total_score = score1+score2+score3';
$BODY$
language plpgsql;

(Not tested, so there might be syntax errors in there)