Note that I removed your right join since your where clause logically and practically makes it an inner join.

It might nonetheless have been deliberate - sometimes swapping between inner and outer joins with identical meaning makes a significant difference to performance. (A perfect query optimiser would be aware that the two forms produced the same results and create the same plan for either, which would remove this tuning opportunity from the developer, but there is of course no such thing as a theoretically perfect query optimiser.)

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Tim Ward