mysql - 如何从一个表中选择不应存在其他记录的记录

Question

我有两张 table 。 subjectTbl 和SubjectAllotTbl。

这是我的主题表

+------------+--------------+---------------------+--------------+--------+----------+
| Subject_Id | Subject_Code | Subject_Name        | Periods_Week | Dep_Id | Semester |
+------------+--------------+---------------------+--------------+--------+----------+
|          1 |         6012 | Basic Electronics   |           10 |      1 |        1 |
|          2 |         5412 | Computer Science    |            7 |      1 |        3 |
|          3 |         1421 | Musical Science     |            4 |      1 |        5 |
|          4 |          547 | Network Programming |            7 |      1 |        5 |
+------------+--------------+---------------------+--------------+--------+----------+

和SubjectAllotTbl

+------------+------------+
| Subject_Id | Teacher_Id |
+------------+------------+
|          1 |          1 |
|          2 |          3 |
|          3 |          2 |
+------------+------------+

我想要做的就是从表SubjectTbl中选择Subject_Name，其中相同的subject_id不应出现在SubjectAllotTbl中

我正在使用 MySql

Answer 1

select subject_name
from SubjectTbl
where subject_id not in ( select distinct subject_id from SubjectAllotTbl)

您可能不需要不同的，除非 subject_id 在不同的 Teacher_id 的SubjectAllotTbl 中重复