Q&A
Q&ACan an index on (a, b, c) efficiently serve a query filtering only b and c?
Usually the leading-column prefix matters; validate any skip-scan behavior on the target engine.
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A composite B-tree is generally organized by its leading column, so omitting a can prevent efficient use of the index for b/c-only predicates. Some engines and versions may use skip scans under particular statistics, but do not assume it. Compare a candidate (b, c) index with the existing index using representative plans and write-cost measurements.