A Query Does Not Use Expected Indexes When Comparing a Field to a Variable
(Doc ID 2242395.1)
Last updated on MARCH 09, 2017
Applies to:MySQL Server - Version 5.1 and later
Information in this document applies to any platform.
A query which compares a string field (CHAR, VARCHAR, or TEXT) to a constant uses an index on that field. A similar query inside a stored procedure or function fails to use the index when comparing the field to a local variable.
For example, this query may use an index:
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