Question

I have a query in which i am Using 13 LEFT OUTER JOINS .The very left table has a large data,so it takes very much time to execute the query and return the result.
But when I am using a where clause to filter the result , It takes very less time.
Now i am confused about which executes first :the joins which produces result and then where clause filters from it OR first it filters the result the takes the join of the result.

Answer 1

Generally, any DBMS (such as SQL) will do its own query optimization, which uses the algorithm it thinks is the fastest. So it’s filtering, then joining.