通过表

Question

我目前正在尝试查询仅为数量少于40的个人显示Num，Surname，ID和Mod。我的主要问题是将这些字段连接在一起，因为这些字段分为2个表和连接Num＆amp;的方法。姓氏和身份证的姓氏Mod需要通过另一个表来链接Num＆amp; ID。

这是我的表格

T1

+-----+-----+--------+
| Num | ID  | amount |
+-----+-----+--------+
| 001 | PC3 |     44 |
| 002 | PC4 |     98 |
| 004 | PC4 |     56 |
+-----+-----+--------+

T2

+-----+---------+
| Num | Surname |
+-----+---------+
| 001 | Balls   |
| 002 | Martin  |
| 004 | Grey    |
+-----+---------+

T3

   +-----+------+
   | ID  | Mod  |
   +-----+------+
   | PC3 | HTML |
   | PC4 | PHP  |
   | PC5 | CSS  |
   +-----+------+

我正在思考

的内容

SELECT t2.Num, t2.Surname, t3.ID, t3.Mod
FROM t2
INNER JOIN t1 ON t1.Num = t2.Num 
INNER JOIN t3 ON t3.ID = t1.ID
WHERE t1.amount = <40;

Answer 1

删除t1.amount和它将起作用的数值之间的'='

SELECT t1.Num, t2.Surname, t1.ID, t3.Mod FROM t2 INNER JOIN t1 ON t1.Num = t2.Num INNER JOIN t3 ON t3.ID = t1.ID WHERE t1.amount < 40

See it from here