update 与select嵌套

1.用b表的结果为a表赋值

update student set hobby= (select hobby_name from hobby )

错误，提示“Subquery return more than one row"

update student set hobby= (select hobby_name from hobby limit 1)

执行ok

说明：查询结果应该是一个唯一字段才能给前面的a表字段赋值。

 

2.用一个表的查询结果给字段赋值

update student set hobby= (select hobby from student where studentid=1) where studentid=2

错误，提示You can't specify target table 'student' for update in FROM clause

解决办法：把查询结果作为临时表b,再次查询赋值

update student set hobby=

(select b.hobby from

(select hobby from student where studentid=1) as b

)

where studentid=2

执行ok

3.用同一个表的查询结果作为条件

update student set status =2 where studentid in( select studentid from student where studentid<10 and status=0 order by studentid asc limit 0,1)

错误，提示#1235 - This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'

update student set status =2 where studentid in( select studentid from student where studentid<10 and status=0 order by studentid asc )

错误，提示You can't specify target table 'student' for update in FROM clause

解决办法：

改变查询方式，

 

update student set status =2 where studentid<10 and status=0 order by studentid asc limit 0,1

   或把查询结果作为临时表b

update student a,( select studentid from student where studentid<10 and status=0 order by studentid asc limit 0,1) b set a.status =2 where a.studentid=b.studentid

 

或连接

update student a join ( select studentid from student where studentid<10 and status=0 order by studentid asc limit 0,1) b on a.studentid=b.studentid set a.status =2