Why MySQL Query Cache Fails: 10 Common Scenarios Explained
This article explains how MySQL's query cache works, why it uses the full SQL statement as a key, and lists ten typical situations—such as using SQL_NO_CACHE, volatile functions, or locks—that prevent a query from being cached.
MySQL's Query Cache stores results based on the exact SQL statement; any difference—even a case change or extra space—creates a separate cache entry.
Scenarios where caching does not occur
Adding the SQL_NO_CACHE hint to the query.
Using functions that return variable values, including built‑in or user‑defined ones such as CURDATE(), GET_LOCK(), RAND(), CONVERT_TZ(), etc.
Querying system databases like mysql or information_schema.
Referencing session‑level variables or local variables inside stored procedures.
Executing statements that acquire locks, e.g., LOCK IN SHARE MODE or FOR UPDATE.
Using SELECT … INTO to export data.
Operating on temporary tables.
Queries that generate warnings.
Statements that do not involve any tables or views.
Queries run by users who only have column‑level privileges.
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