如果我运行简单的查询，它会很快完成：
explain select * from my_data where id in (132730151);
+----+-------------+---------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------+-------+---------------+---------+---------+-------+------+-------+
| 1 | SIMPLE | my_data | const | PRIMARY | PRIMARY | 4 | const | 1 | |
+----+-------------+---------+-------+---------------+---------+---------+-------+------+-------+
如果我使用子查询运行基本相同的查询，它似乎永远不会完成：
explain select * from my_data where id in (select my_data_id from my_other_data where id = 46855459);
+----+--------------------+---------------+-------+--------------------------+---------+---------+-------+-----------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+---------------+-------+--------------------------+---------+---------+-------+-----------+-------------+
| 1 | PRIMARY | my_data | ALL | NULL | NULL | NULL | NULL | 132862517 | Using where |
| 2 | DEPENDENT SUBQUERY | my_other_data | const | PRIMARY,my_data_id_index | PRIMARY | 4 | const | 1 | |
+----+--------------------+---------------+-------+--------------------------+---------+---------+-------+-----------+-------------+
对于这种情况，似乎MySQL正在经历每一行。为什么没有mysql在第二种情况下使用id的主索引？
我的例子有点做作。我实际上使用mysqldump导出一系列数据，这是最简单的情况。由于我使用mysqldump，我无法将其转换为连接，因为我只能访问where子句。