More than Two Levels

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If the hierarchy consists of more than two levels, you should use the same filtering technique for the lower levels. For each extra level, you need one additional JOIN clause or subquery, working yourself up the hierarchy tree until you reach the upper level to specify exactly the same WHERE clause for every level included, or at least until you find a denormalized copy of the column you need to filter on. Denormalization could help you achieve better performance for multilevel hierarchical recordsets. But before you denormalize, make sure you really need to. The relational systems of today are fast; maybe yours is fast enough even for the multilevel joins you need if you don't denormalize.