Question

我有两张桌子f1和s1。我必须比较两个表的乐队列，如果它相同，那么我必须更新＆＃39;没有变化＆＃39;在s1的状态列中，如果它不相同，那么等级改变＆＃39;。

mysql> select * from f1;
+--------+------+------+-------------+
| emp_id | name | band | project_des |
+--------+------+------+-------------+
| 1      | A    | u1   | IT          |
| 2      | B    | u2   | COMP        |
| 4      | D    | u3   | COMP        |
| 5      | E    | u2   | ELECTRICAL  |
| 6      | F    | u2   | IT          |
| 8      | H    | p1   | MECH        |
+--------+------+------+-------------+
6 rows in set (0.00 sec)

mysql> select * from s1;
+--------+------+------+-------------+--------------+--------+
| emp_id | name | band | project_des | check_status | status |
+--------+------+------+-------------+--------------+--------+
| 1      | A    | u1   | IT          | present      | NULL   |
| 2      | B    | u1   | COMP        | present      | NULL   |
| 3      | C    | p2   | COMP        | NULL         | NULL   |
| 4      | D    | p2   | ELECTRICAL  | present      | NULL   |
| 5      | E    | p3   | IT          | present      | NULL   |
| 7      | G    | p3   | IT          | NULL         | NULL   |
| 8      | H    | p1   | COMP        | present      | NULL   |
+--------+------+------+-------------+--------------+--------+
7 rows in set (0.00 sec)

mysql> update s1 inner join f1 on 's1.band' != 'f1.band' set status='grade change';
Query OK, 4 rows affected (0.06 sec)
Rows matched: 7  Changed: 4  Warnings: 0

mysql> select * from s1;
+--------+------+------+-------------+--------------+--------------+
| emp_id | name | band | project_des | check_status | status       |
+--------+------+------+-------------+--------------+--------------+
| 1      | A    | u1   | IT          | present      | grade change |
| 2      | B    | u1   | COMP        | present      | grade change |
| 3      | C    | p2   | COMP        | NULL         | grade change |
| 4      | D    | p2   | ELECTRICAL  | present      | grade change |
| 5      | E    | p3   | IT          | present      | grade change |
| 7      | G    | p3   | IT          | NULL         | grade change |
| 8      | H    | p1   | COMP        | present      | grade change |
+--------+------+------+-------------+--------------+--------------+
7 rows in set (0.00 sec)

请帮我找一下我做错了什么。

Answer 1

在SQL Server上，试试这个：

update s1 set
    status = case when f1.band = s1.band
        then 'no change' else 'grade change' end
from s1 join f1 on f1.emp_id = s1.emp_id

或者，在mySQL上，如果该语法不起作用：

update s1 set status = 
    (Select case when band = s1.band
     then 'no change' else 'grade change' end
     From f1 where emp_id = s1.emp_id)

Answer 2

UPDATE table1, table2 SET table1.Column = table2.Column 
WHERE table1.Column  = table2.Column

如何通过比较两个表中的两列来更新表中的列

2 个答案: