query has no destination for result data in a function that has a set of instructions in postgresql - sql

Question

I am trying to automate a set of sentences that I execute several times a day. For this I want to put them in a postgres function and just call the function to execute the sentences consecutively. If everything runs OK then in the end return the SUCCESS value. The following function replicates my idea and the error I am getting when executing the function:
CREATE OR REPLACE FUNCTION createTable() RETURNS int AS $$
BEGIN
DROP TABLE IF EXISTS MY_TABLE;
CREATE TABLE MY_TABLE
(
ID integer
)
WITH (
OIDS=FALSE
);
insert into MY_TABLE values(1);
select * from MY_TABLE;
RETURN 'SUCCESS';
END;
$$ LANGUAGE plpgsql;
Invocation:
select * from createTable();
With my ignorance of postgresql I would expect to obtain the SUCCESS value as a return (If everything runs without errors). But the returned message causes me confusion, isn't it the same as a function in any other programming language? When executing the function I get the following message:
query has no destination for result data Hint: If you want to
discard the results of a SELECT, use PERFORM instead.

Answer 1

query has no destination for result data Hint: If you want to discard the results of a SELECT, use PERFORM instead.
You are getting this error because you do not assign the results to any variable in the function. In a function, you would typically do something like this instead:
select * into var1 from MY_TABLE;
Therefore, your function would look something like this:
CREATE OR REPLACE FUNCTION createTable() RETURNS int AS $$
DECLARE
var1 my_table%ROWTYPE;
BEGIN
DROP TABLE IF EXISTS MY_TABLE;
CREATE TABLE MY_TABLE
(
ID integer
)
WITH (
OIDS=FALSE
);
insert into MY_TABLE values(1);
select * into var1 from MY_TABLE;
<do something with var1>
RETURN 'SUCCESS';
END;
$$ LANGUAGE plpgsql;
Otherwise, if you don't put the results into a variable, then you're likely hoping to achieve some side effect (like advancing a sequence or firing a trigger somehow). In that case, plpgsql expects you to use PERFORM instead of SELECT
Also, BTW your function RETURNS int but at the bottom of your definition you RETURN 'SUCCESS'. SUCCESS is a text type, not an int, so you will eventually get this error once you get past that first error message -- be sure to change it as necessary.