我们如何模拟 MySQL MINUS 查询?
mysqlmysqli database
由于我们无法在 MySQL 中使用 MINUS 查询，我们将使用 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，它们具有以下数据 −
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)
现在，以下使用 JOINS 的查询将模拟 MINUS 以返回 student_info 表中但不返回 Student_detail 表中的 ‘studentid’ 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)
现在，以下查询将给出与上述查询相反的结果，即它将返回 student_detail 中的‘studentid’值，但不返回 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)
