數據庫原理學習記錄2

數據庫原理學習記錄2

問題1：You can’t specify target table ‘student’ for update in FROM clause

通過百度翻譯：

參考博客：
https://blog.csdn.net/qq_29672495/article/details/72668008

該文提出**“將SELECT出的結果再通過中間表SELECT一遍”**

模仿嘗試：

例1：

delete from student
where 姓名=any(
select student.姓名
from (select student.姓名
from student left join score
on student.學號=score.學號
where score.課號 is null) student
);
Query OK, 8 rows affected (0.01 sec)

例2：

mysql> delete from teacher
    -> where 工資<(
    -> select avg(工資)
    -> from teacher
    -> );
ERROR 1093 (HY000): You can't specify target table 'teacher' for update in FROM clause
mysql> delete from teacher
    -> where 工資<any(
    -> select avg(工資)
    -> from teacher
    -> );
ERROR 1093 (HY000): You can't specify target table 'teacher' for update in FROM clause
mysql> delete from teacher
    -> where 工資<(
    -> select avg(工資)
    -> from (select avg(工資) from teacher)teacher
    -> );
Query OK, 0 rows affected (0.00 sec)

問題2：Subquery returns more than 1 row

通過百度翻譯：

資料查找：
https://zhidao.baidu.com/question/327417776459413245.html

mysql> delete from student
    -> where 姓名=(
    -> select student.姓名
    -> from (select student.姓名
    -> from student left join score
    -> on student.學號=score.學號
    -> where score.課號 is null) student
    -> );
ERROR 1242 (21000): Subquery returns more than 1 row
mysql> delete from student
    -> where 姓名=any(        //此處添加 any
    -> select student.姓名
    -> from (select student.姓名
    -> from student left join score
    -> on student.學號=score.學號
    -> where score.課號 is null) student
    -> );
Query OK, 8 rows affected (0.01 sec)

問題3：Every derived table must have its own alias

通過百度翻譯：每個派生表都必須有自己的別名
在解決問題1，進行再select時容易出現
解決方法：取別名

問題4：Cannot delete or update a parent row: a foreign key constraint fails

百度翻譯：無法刪除或更新父行：外鍵約束失敗
原因：老師故意挖的坑
解決方法：取消外鍵，迅速刪除，接上外鍵，一氣呵成

參考博客：
https://blog.csdn.net/qq_39403545/article/details/86649026