Erik Darling gives us a scenario where OUTER APPLY is quite useful:
In all, this query will run for about 18 seconds. The majority of it is spent in a bad neighborhood.
Why does this suck? Boy oh boy. Where do we start?
– Sorting the Votes table to support a Merge Join?
– Choosing Parallel Merge Joins ever?
– Choosing a Many To Many Merge Join ever?
– All of the above?
I voted “all of the above.” Click through to see how Erik turns a bad query plan into a much less bad query plan.