"SHOW ..." statements update "Rows_fetched" value in "information_schema.user_statistics"

[Yura Sorokin]

When user stats are enabled ("SET GLOBAL userstat = ON"), after executing any statement of the "SHOW ..." family that produces non-empty result, the total number of the sent rows ("Rown_fetched") is updated in the "information_schema.user_statistics".

This happens because of the invalid "if" condition in the "void THD::update_stats(bool ran_command)" ("sql_class.cc")
**************************************************************************
      else if (!sql_command_flags[lex->sql_command] & CF_STATUS_COMMAND)
**************************************************************************
which is always "false" and therefore gets optimized out.

[Yura Sorokin (yura-sorokin)]

Also, this condition is considered suspicious and generates compiler's warning on newer versions of GCC (observed on 5.2.1 , Ubuntu 15.10 64-bit).
This could lead to build failures when"-Werror" is enabled.

[Laurynas Biveinis (laurynas-biveinis)]

https://github.com/percona/percona-server/pull/212, https://github.com/percona/percona-server/pull/213

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-937