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Indexing Overkill

Indexing Overkill

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Question:
If a table has a primary key on columns A, B, and C, is there any advantage to also defining an index on columns A and B? Wouldn’t the optimizer use the prime key even if only the first two columns were included in the Where clause?

Answer:
Your grasp of the applicability of the index is 100 percent for SQL 6.5, but I don’t think it matters in SQL 7. There is no necessity to create the “short” version of the index, as the optimizer will use the primary index (provided that the order of the keys in the index is observed).

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