4126
MySQLERRORNotableHIGH confidence
BLOB/TEXT column used without key length in index
Production Risk
Low — DDL fails; no data is affected.
Why it happens
- 1An index was created on a BLOB or TEXT column without specifying a prefix length.
Fix
Specify a key prefix length
Specify a key prefix length
ALTER TABLE t ADD INDEX idx_col (col(255));
Why this works
A prefix length tells MySQL how many characters to use from the beginning of the BLOB/TEXT column for indexing.
What not to do
✕
Sources
Official documentation ↗
MySQL 8.0 — 4126 ER_BLOB_USED_AS_KEY2
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