Why MySQL Indexes Fail: 8 Common Limitations You Must Know
This article outlines eight key MySQL index usage restrictions, including key length limits, unsupported data types, lack of functional and hash indexes, and conditions that prevent the optimizer from leveraging indexes, helping developers avoid performance pitfalls.
Below are the current limitations related to index usage in MySQL:
The total length of index keys for the MyISAM storage engine cannot exceed 1000 bytes.
Columns of type BLOB and TEXT can only have prefix indexes.
MySQL does not currently support functional indexes.
When using the not‑equal operators (!= or <>), MySQL cannot use an index.
If a filter column is wrapped in a function (e.g., abs(column)), MySQL cannot use an index.
In JOIN statements, if the join‑condition columns have mismatched data types, MySQL cannot use an index.
When using LIKE with a pattern that starts with a wildcard (e.g., '%abc...'), MySQL cannot use an index.
Non‑equality queries cannot use hash indexes in MySQL.
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