In C, the classic short cut evalution might be something like
if ( a != NULL && a->b == 0 )…
to avoid evaluating a structure reference if invalid…

I’m trying something similar in a postgresql trigger:

IF TG_TABLE_NAME::text != 'collection_item' OR OLD.domain = 'HERB' OR NEW.domain = 'HERB' THEN
  ... blah
END IF;

So if the table is collection_item it contains the field domain, but other tables don’t have that field. So in theory if table is not collection_item, it should short circuit and not evaluate OLD.domain. However this wasn’t working, it would give an error that

`ERROR: record “old” has no field “domain”

So I read here about evaluation rules,

https://www.postgresql.org/docs/9.0/sql-expressions.html#SYNTAX-EXPRESS-EVAL

It implies that if you encounter this problem you can get around it with CASE. So I tried that…

IF (CASE WHEN TG_TABLE_NAME::text != 'collection_item' THEN true WHEN OLD.domain = 'HERB' OR NEW.domain = 'HERB' THEN true ELSE false END) THEN
... blah
END IF;

but I still get “ERROR: record “old” has no field “domain”`

I can get around it with nesting IFs…

IF  TG_TABLE_NAME::text = 'collection_item' THEN
    IF OLD.domain = 'HERB' OR NEW.domain = 'HERB' THEN
        is_target := true;
    END IF;
ELSE
    is_target := true;
END IF;

But I’m curious why my other attempts don’t work.

I’m expecting short cut evalution to work.