Question

I probably didn’t word the question right buy I have a query that is taking a substantial amount of time because of ‘or’.

select stuff 
from table1 T1
left join table2 T2 on T2.field1 = T1.field or T2.field2 = T1.field
where some condition

I have to check both fields to join. Is there a better way to do this?

Answer 1

There’s two options I can think of based on what’s provided:

Use IN instead

   select stuff 
     from table1 T1
left join table2 T2 on T1.field IN (T2.field1, T2.field2)
    where some condition

Using a UNION

Mind that I used UNION ALL–it’s faster than UNION, but UNION removes duplicates so alter to suit your needs:

   select stuff 
     from table1 T1
left join table2 T2 on T1.field = T2.field1
    where some condition
UNION ALL
   select stuff 
     from table1 T1
left join table2 T2 on T1.field = T2.field2
    where some condition