The original title is: "Why Your Database Index Gets Ignored (and How to Design One That Isn't)"

Short summary

Multi-column database indexes only work when queries filter starting from the index's left-most column (the left-prefix rule). Reorganize indexes so filter columns come first, then add all needed columns to create covering indexes that eliminate table lookups. Each index taxes writes, so design them strategically based on actual query patterns.

• •Multi-column indexes only serve queries filtering from the leftmost column (left-prefix rule)
• •Reorder index columns so most-filtered columns come first for better query usage
• •Use covering indexes that include all query columns to eliminate expensive table lookups

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