Getting Error "query has no destination for result data"

Question

I trying to select query based on condition using IF ElSE in postgres. Below is my query.

DO
$do$
DECLARE res varchar(50) := 'a';
BEGIN
IF (res = 'a') THEN
SELECT "Name" FROM "TestTable";
ELSE 
SELECT "ID" FROM "TestTable";
END IF;
END
$do$

but I am getting following error

ERROR:  query has no destination for result data
HINT:  If you want to discard the results of a SELECT, use PERFORM instead.
CONTEXT:  PL/pgSQL function inline_code_block line 5 at SQL statement

What I am doing wrong here??

Answer 1

DO purpose is to execute anonymous code block and it doesn't return anything (it returns void, to be specific).

You can execute your SELECT statement afterwards (outside of DO block), or perform an INSERT to temporary table which you need to create beforehand (and this can be done within the block).