Re: What does Postgresql do when using CASE WHEN without ELSE?

[Seref Arikan <serefarikan@xxxxxxxxxxxxxxxxxxxxx>]

Apologies, I found the answer in the documentation:

http://www.postgresql.org/docs/9.0/static/functions-conditional.html says:

"If the ELSE clause is omitted and no condition is true, the result is null."

Best regards

Seref

On Tue, Feb 12, 2013 at 10:39 AM, Seref Arikan <serefarikan@xxxxxxxxxxxxxxxxxxxxx> wrote:

Greetings, 

I want to use CASE WHEN to make sure that I don't try to call a function on a row that does not exist. This is used within a WHERE statement as follows (without the function call I've mentioned);

WHERE

      CASE WHEN EXISTS(SELECT ATRNODE.featuremappingid from ELEMENT1, ATRNODE where ELEMENT1.pathstring || '/' || 'name/value' = ATRNODE.pathstring)

      THEN

      (   ELEMENT1.pathstring || '/' || 'name/value' = ATRNODE.pathstring

          and

          ATRNODE.valstring = 'Måltillstånd' --this will be where the function is going to be used

      )

      ELSE

       ELEMENT1.id = -1291927189371983619872981729

      END

   

The overall mechanism lets me apply a constraint so that if a row does not exist, the query returns no results, without attempting to process ATRNODE.valstring value (which represents more complicated info that will exist in the row in other cases)

The thing is, when I omit the ELSE, the query still returns no results if the row does not exist. It is as if an ELSE statement is added with an impossible constraint, just like the one I'm explicitly providing.

 I'm keeping the ELSE so that I explicitly introduce a where statement that will not correspond to any rows, but what is happening when I omit ELSE, so that the query still functions as it should?

Best regards

Seref