MySQL Bugs: #38251: Useless external queries should be ignored

Bug #38251	Useless external queries should be ignored
Submitted:	21 Jul 2008 0:29	Modified:	21 Jul 2008 13:13
Reporter:	Federico Razzoli (OCA)	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Optimizer	Severity:	S5 (Performance)
Version:	5.0.51	OS:	Any
Assigned to:	Assigned Account	CPU Architecture:	Any

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Description:
When using a derived table, the external query in some cases may be useless. In my opinion, the optimizer should detect those cases and ignore useless queries. See the examples below.

How to repeat:
EXPLAIN SELECT t.* FROM (SELECT * FROM INFORMATION_SCHEMA.CHARACTER_SETS) AS t

EXPLAIN SELECT t.* FROM (SELECT * FROM INFORMATION_SCHEMA.CHARACTER_SETS ORDER BY 2) AS t ORDER BY 1

Thank you for a reasonable feature request.