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If you have a clustered (or covering) index starting with (Key1, Key2, Key3, ...) on the table that the CTE is querying, this should be a well-performing query. Can you add a "Key4", preferably an identity column, in the source table to your non-unique clustered index, so you perhaps can make the index unique? That way, you could also set "Key4" as your ...


It makes no difference: the optimiser evaluates the query and will work out predicate order for itself, matching a suitable index and all the other good stuff it does. This is because SQL is "declarative" not "procedural": you say what you want, not how to do it. It's nicer to read though...

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