PostgreSQL - Loop through alternative query results

Question

On PostgreSQL, I am trying to loop through alternative query results.

I have this solution working:

FOR target
IN query
LOOP
  statements
END LOOP;

But I want to do something like this:

FOR target
IN (IF condition_1
    THEN query_1
    ELSE query_2
    END IF)
LOOP
  statements
END LOOP;

However I cannot make it to work. I have also tried this version but it's also not working:

FOR target
IN (CASE
      WHEN condition_1 THEN query_1
      ELSE query_2
    END)
LOOP
  statements
END LOOP;

Is there any way of implementing this behavior in PostgreSQL?

Thanks!

Lukasz Szozda · Accepted Answer · 2021-01-08 15:31:54Z

1

You could use:

FOR target
IN (SELECT ... FROM ... WHERE     condition1
    UNION ALL
    SELECT ... FROM ... WHERE NOT condition1)
LOOP
  statements
END LOOP;

Queries: query1 and query2 are combined with UNION ALL but condition will pass only single part depending of value.

answered Jan 8, 2021 at 15:31

Lukasz Szozda

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4 Comments

Thanks for the tip Lukasz, I will try your suggestion!

I could make it to work. Once again thank you so much Lukasz!

I'm sorry @Luckasz, it was my first question here and I didn't know about accepting answers. I have accepted it now :)