Why MySQL Unique Indexes Still Allow Duplicates and How to Fix Them

This article explains why a MySQL 8 InnoDB table with a unique index can still store duplicate rows—especially when indexed columns contain NULL or when logical deletion is used—and presents several practical strategies, including status counters, timestamps, extra IDs, hash fields, and batch‑insert techniques, to enforce true uniqueness.

Batch InsertHash FieldInnoDB

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Why MySQL Unique Indexes Still Allow Duplicates and How to Fix Them