Suppose there are two huge tables: a and b.
How to build index to improve the performance for this query:
select * from a join b on a.a1= b.b1
With a clustered index on the two column you are joining on, you might get Merge Join rather than a Hash Join for some marginal performance improvement.
More likely you should take a step back and ask yourself why you are running this query at all, and particularly if you want SELECT *.
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