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Why does column order matter in a composite index?

Q: Why does column order matter in a composite index?

## Composite Index Column Order — The Left-Prefix Rule A **composite index** (multi-column index) is a B-Tree sorted by the first column, then by the second within each group of the first, and so on. The database can only use the index starting from the **leftmost** columns — this is the **left-prefix rule**. INDEX(status, customer_id, amount) <rect class='d-box-accent' x='0' y='0' width='130

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