When should I use an INNER -LOOP- JOIN instead of

Question

Today I learned about a thing in SQL Server called INNER LOOP JOIN.

What does this mean? (Google is not helping .. or should I say ... the blog posts about it are a bit .. technical and are blowing my mind).

Also, what are some common scenarios that would be a good idea to use an INNER LOOP JOIN over a standard INNER JOIN?

Answer 1

LOOP | HASH | MERGE are Join hints, specifying that the join in the query should use looping, hashing, or merging. Using LOOP |HASH | MERGE JOIN enforces a particular join between two tables. LOOP cannot be specified together with RIGHT or FULL as a join type.

You should always use INNER JOIN. Let the query optimizer decide whether it wants to do a LOOP, MERGE, or HASH join. In almost all cases the optimizer will make a better judgement. Which one will be used and when can be found from my presentation http://sqlbits.com/Sessions/Event4/Understanding_Graphical_Execution_Plans.

Answer 2

What you are referring to is a join hint. Like other hints, join hints should only be specified as a last resort as most of the time SQL server would pick correct algorithm. A good article to explain some of it is this.