Bug #79717 Document Bug about "EXPLAIN Output Format"

• Submitted: 21 Dec 2015 2:47
• Modified: 26 Feb 2016 0:13
• Reporter: Yoshiaki Yamasaki
• Status: Closed
• Category: MySQL Server: Documentation
• Severity: S3 (Non-critical)
• Version: 5.7
• OS: Any
• Assigned to: Paul DuBois
• CPU Architecture: Any
• Tags: explain

[21 Dec 2015 2:47] Yoshiaki Yamasaki

Description:
[Target Document]
https://dev.mysql.com/doc/refman/5.7/en/explain-output.html#explain-join-types
https://dev.mysql.com/doc/refman/5.6/en/explain-output.html#explain-join-types
https://dev.mysql.com/doc/refman/5.5/en/explain-output.html#explain-join-types
https://dev.mysql.com/doc/refman/5.1/en/explain-output.html#explain-join-types
https://dev.mysql.com/doc/refman/5.0/en/explain-output.html#explain-join-types
 => Description of "unique_subquery" part

[Detail]
I think description of unique_subquery is wrong as follows.

 Now              : This type replaces ref for some IN subqueries of the following form: 
 Modified version : This type replaces const for some IN subqueries of the following form: 

Because unique_subquery use primary key or unique key. Therefore, I think "ref" is worng. I think "const" is correct.

How to repeat:
N/A

Suggested fix:
Please see Description.

[21 Dec 2015 9:11] MySQL Verification Team

Thank you for the bug report.

[25 Feb 2016 16:34] Paul DuBois

Comment from one of the optimizer developers:

I think it should be:

This type replaces eq_ref for some IN subqueries of the following form:

const means that the value is constant in optimization phase.  AFAICT, this is not the case here.  In this case, there may be multiple index look-ups for different values.

[25 Feb 2016 16:35] 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.

[26 Feb 2016 0:13] Yoshiaki Yamasaki

Hi Paul,

Thank you! I checked the modified document.