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For example which is better:
select * from t1, t2 where t1.country='US' and t2.country=t1.country and t1.id=t2.id or
select * from t1, t2 where t1.country'US' and t2.country='US' and t1.id=t2.id better as in less work for the database, faster results.
Note: Sybase, and there’s an index on both tables of country+id.
I had a situation similar to this and this was the solution I resorted to:
Select * FROM t1 INNER JOIN t2 ON t1.id = t2.id AND t1.country = t2.country AND t1.country = ‘US’
I noticed that my query ran faster in this scenario. I made the assumption that joining on the constant saved the engine time because the WHERE clause will execute at the end. Joining and then filtering by ‘US’ means you still pulled all the other countries from your table and then had to filter out the ones you wanted. This method pulls less records in the end, because it will only find US records.