MySQL更新错误1093

这适用于doc_id是主键的表：

select count(*)+1 from doctor where 
exp > (select exp from doctor where doc_id='001');

+------------+
| count(*)+1 |
+------------+
|          2 |
+------------+

但是,当我使用相同的选择查询在表中设置字段时,它会报告以下错误：

update doctor set rank=
(  select count(*)+1 from doctor where 
   exp > (select exp from doctor where doc_id='001')
) where doc_id='001';

ERROR 1093 (HY000): You can't specify target table 'doctor' for update 
in FROM clause

我无法理解它正在讨论哪个目标表引用.谁能解释一下？

最佳答案

此限制记录在MySQL manual中：

Currently,you cannot update a table and select from the same table in a subquery.

作为一种变通方法,您可以将子查询包装在另一个子查询中并避免该错误：

update doctor set rank=
(select rank from (  select count(*)+1 as rank from doctor where 
   exp > (select exp from doctor where doc_id='001')
) as sub_query) where doc_id='001';