MySQL Bugs: #4816: Composite index with blob column returns no results with null comparison

Bug #4816	Composite index with blob column returns no results with null comparison
Submitted:	29 Jul 2004 23:34	Modified:	1 Aug 2004 15:10
Reporter:	Dean Ellis
Status:	Closed
Category:	Server: MyISAM	Severity:	S1 (Critical)
Version:	4.0	OS:
Assigned to:	Sergei Golubchik	Target Version:

Description:
Composite index covering blob column and char/varchar column returns no results with null
comparison against the blob.

How to repeat:
DROP TABLE IF EXISTS t1;
CREATE TABLE t1 ( a tinytext, b char(1), INDEX idx (a(1),b) );
INSERT INTO t1 VALUES (NULL,''), (NULL,'');
SELECT COUNT(*) FROM t1 USE INDEX (idx) WHERE a IS NULL;
DROP TABLE t1;

Suggested fix:
n/a

Thank you for your bug report. This issue has been committed to our
source repository of that product and will be incorporated into the
next release.

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available version, including the bugfix, yourself. More information 
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Additional info:

fixed in 4.0.21