小编0x8*_*x89的帖子

免责声明：请原谅我对数据库内部知识的缺乏。它是这样的：

我们运行一个应用程序（不是我们编写的），它在数据库的定期清理作业中存在很大的性能问题。查询如下所示：

delete from VARIABLE_SUBSTITUTION where BUILDRESULTSUMMARY_ID in (
       select BUILDRESULTSUMMARY_ID from BUILDRESULTSUMMARY
       where BUILDRESULTSUMMARY.BUILD_KEY = "BAM-1");

直截了当、易于阅读和标准 SQL。但不幸的是非常慢。解释查询显示VARIABLE_SUBSTITUTION.BUILDRESULTSUMMARY_ID未使用现有索引：

mysql> explain delete from VARIABLE_SUBSTITUTION where BUILDRESULTSUMMARY_ID in (
    ->        select BUILDRESULTSUMMARY_ID from BUILDRESULTSUMMARY
    ->        where BUILDRESULTSUMMARY.BUILD_KEY = "BAM-1");
| id | select_type        | table                 | type            | possible_keys                    | key     | key_len | ref  | rows    | Extra       |
+----+--------------------+-----------------------+-----------------+----------------------------------+---------+---------+------+---------+-------------+
|  1 | PRIMARY            | VARIABLE_SUBSTITUTION | ALL             | NULL                             | NULL    | NULL    | NULL | 7300039 …