由于我们无法在 MySQL 中使用 MINUS 查询，因此我们将使用 LEFT JOIN 来模拟 MINUS 查询。可以借助以下示例来理解：
示例
在此示例中，我们有两个表，即 Student_detail 和 Student_info，其内容如下数据 -
mysql> Select * from Student_detail;
+-----------+---------+------------+------------+
| studentid | Name | Address | Subject |
+-----------+---------+------------+------------+
| 101 | YashPal | Amritsar | History |
| 105 | Gaurav | Chandigarh | Literature |
| 130 | Ram | Jhansi | Computers |
| 132 | Shyam | Chandigarh | Economics |
| 133 | Mohan | Delhi | Computers |
| 150 | Rajesh | Jaipur | Yoga |
| 160 | Pradeep | Kochi | Hindi |
+-----------+---------+------------+------------+
7 rows in set (0.00 sec)
mysql> Select * from Student_info;
+-----------+-----------+------------+-------------+
| studentid | Name | Address | Subject |
+-----------+-----------+------------+-------------+
| 101 | YashPal | Amritsar | History |
| 105 | Gaurav | Chandigarh | Literature |
| 130 | Ram | Jhansi | Computers |
| 132 | Shyam | Chandigarh | Economics |
| 133 | Mohan | Delhi | Computers |
| 165 | Abhimanyu | Calcutta | Electronics |
+-----------+-----------+------------+-------------+
6 rows in set (0.00 sec)
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现在，以下使用 LEFT JOIN 的查询将模拟 MINUS 以返回 Student_info 中的“studentid”值，但不返回 Student_detail 表中的值。
mysql> SELECT studentid from student_info LEFT JOIN Student_detail USING(studentid) WHERE student_detail.studentid IS NULL;
+-----------+
| studentid |
+-----------+
| 165 |
+-----------+
1 row in set (0.07 sec)
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现在，以下查询将为我们提供与上述查询相反的结果，即它将返回 Student_detail 中的“studentid”值，但不会返回 Student_info 表中的值。
mysql> SELECT studentid from student_detail LEFT JOIN Student_info USING(studentid) WHERE student_info.studentid IS NULL;
+-----------+
| studentid |
+-----------+
| 150 |
| 160 |
+-----------+
2 rows in set (0.00 sec)
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