Bug #34933 clarify index_merge usage across multiple tables

• Submitted: 28 Feb 2008 15:35
• Modified: 28 Feb 2008 20:12
• Reporter: Scott Noyes
• Status: Closed
• Category: MySQL Server: Documentation
• Severity: S4 (Feature request)
• Version: 5.0
• OS: Any
• CPU Architecture: Any

[28 Feb 2008 15:35] Scott Noyes

Description:
The documentation regarding the Index Merge method does not make it abundantly clear that it applies only to multiple indexes on a single table, and cannot be used for merging indexes across multiple tables.

For example, this cannot use an index merge:

SELECT * FROM t1 JOIN t2 USING (id) WHERE t1.x = 10 OR t2.y = 20;

How to repeat:
http://dev.mysql.com/doc/refman/5.0/en/index-merge-optimization.html

Suggested fix:
Add the phrase, "from a single table" somewhere on that page.

[28 Feb 2008 20:12] Paul DuBois

Thank you for your bug report. This issue has been addressed in the documentation. The updated documentation will appear on our website shortly, and will be included in the next release of the relevant products.

Added to end of first paragraph on page:

This access method merges index scans from a single table; it does
not merge scans across multiple tables.