[code] select a, b, c from tablea a1 where a1.a IN (select a2.a from table2 a2)
And I have been told by another developer I should put an index on the a2.a column as it will do a full table scan.
I do not have much experience with indexes at all and not sure what type of index I need to put in?
Can someone tell me what type of index and a basic syntax to implement it, or a way to do it in management studio? Reading up on clustered and non-clustered and after reading it doesn't make any sense really to me what it is I need.