MySQL log-queries-not-using-indexes 和 UNION 误报或错误？答案

【问题标题】：MySQL log-queries-not-using-indexes and UNION false positive or error?MySQL log-queries-not-using-indexes 和 UNION 误报或错误？
【发布时间】：2013-07-07 04:33:26
【问题描述】：

我用这个参数激活了慢查询日志：

log_slow_queries = /var/log/mysql/mysql-slow.log
long_query_time = 10
log-queries-not-using-indexes

现在看来 MySQL 只记录没有索引的查询

这是一个日志样本

# Time: 130709 15:33:54
# User@Host: xxxxxx[yyyyyy] @ localhost []
# Query_time: 0.000467  Lock_time: 0.000105 Rows_sent: 1  Rows_examined: 0
SET timestamp=1373376834;
SELECT count(`id`) as `totale` FROM ( SELECT `id` FROM `gg_evento` WHERE `team_home` = 51620 AND `status_home` = 3 AND `status_guest` = 3 UNION ALL SELECT `id` FROM `gg_evento` WHERE `team_guest` = 51620 AND `status_home` = 3 AND `status_guest` = 3) AS sq2 WHERE 1 LIMIT 1;

不过，这个查询已经过优化。

mysql> explain SELECT count(`id`) as `totale` FROM ( SELECT `id` FROM `gg_evento` WHERE `team_home` = 51620 AND `status_home` = 3 AND `status_guest` = 3 UNION ALL SELECT `id` FROM `gg_evento` WHERE `team_guest` = 51620 AND `status_home` = 3 AND `status_guest` = 3) AS sq2 WHERE 1 LIMIT 1\G
*************************** 1. row ***************************
           id: 1
  select_type: PRIMARY
        table: NULL
         type: NULL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: NULL
        Extra: Select tables optimized away
*************************** 2. row ***************************
           id: 2
  select_type: DERIVED
        table: gg_evento
         type: ref
possible_keys: fk_evento_team_home,IDX_PARTITE_NON_TERMINATE,IDX_CARICA_SFIDANTI
          key: fk_evento_team_home
      key_len: 4
          ref: 
         rows: 1
        Extra: Using where
*************************** 3. row ***************************
           id: 3
  select_type: UNION
        table: gg_evento
         type: ref
possible_keys: IDX_TOTALE_GIOCATE_GUEST
          key: IDX_TOTALE_GIOCATE_GUEST
      key_len: 13
          ref: 
         rows: 1
        Extra: Using where; Using index
*************************** 4. row ***************************
           id: NULL
  select_type: UNION RESULT
        table: <union2,3>
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: NULL
        Extra: 
4 rows in set (0.00 sec)

我在 MySQL 文档中看到了这个警告：

This option does not necessarily mean that no index is used

但是……

我不明白记录的查询是否正确，或者我有可以修复的优化问题
万一这个查询是误报，有办法避免mysql记录吗？

似乎 MySQL 将所有包含 UNION 的查询都记录为无索引查询，我对其进行了搜索，但一无所获。

有什么想法吗？谢谢提前米歇尔

【问题讨论】：

这个问题让我很感兴趣……2年后你有什么发现吗？

标签： mysql union sql-optimization mysql-slow-query-log

【解决方案1】：

你可以试试 min_examined_row_limit (https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_min_examined_row_limit)

正如您的示例显示“Rows_examined: 0”，设置 a/m 变量可以抑制日志记录。

set global  min_examined_row_limit = 2;

【讨论】：