EC
1739
MySQLWARNINGCriticalQueryHIGH confidence

Index hint ignored because it is not applicable to the query

Production Risk

Low — warning only; query executes without the hint.

What this means

An index hint (USE INDEX, FORCE INDEX, or IGNORE INDEX) was specified but is not applicable to the given query, so the optimizer ignores it.

Why it happens
  1. 1Specifying USE INDEX for an index that does not exist on the table.
  2. 2Using an ORDER BY index hint with a query that cannot use that index for ordering.
How to reproduce
trigger — this will error
trigger — this will error
SELECT * FROM t USE INDEX (nonexistent_idx) WHERE col = 1;

expected output

Warning (Code 1739): No index named 'nonexistent_idx' was found in table 't'.

Fix

Verify the index name and applicability

Verify the index name and applicability
SHOW INDEX FROM t;
-- Use only index names that appear in the output.

Why this works

Checking existing indexes before specifying hints prevents this warning.

What not to do

✕

Sources
Official documentation ↗

MySQL 8.0 — 1739 ER_WARN_INDEX_NOT_APPLICABLE

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