Reducing select fields hurts query performance
We have a query that looks something like:
select a, b, c, d, e, f
from tbla inner join tblb on tbla.....
This query runs in the expected 200-400 ms range.
If we run the same query but reduce the select to just:
select a
from tbla inner join tblb on tbla.....
then the query runs for 30 minutes or more.
The rest of the query is identical. Is there a logical explanation for how this can happen?
Thanks.