如何借助分组函数 COUNT(*) 和 GROUP BY 子句知道列中某个值的重复次数？

我们可以使用 COUNT(*) 和 GROUP BY 子句来找出列中某个值的重复情况。以下是在“Student”表的“Name”列上使用 COUNT(*) 和 GROUP BY 子句的示例来演示 -

mysql> select count(*),name from student group by name;

+----------+---------+
| count(*) | name    |
+----------+---------+
| 1        | Aarav   |
| 2        | Gaurav  |
| 1        | Harshit |
+----------+---------+

3 rows in set (0.00 sec)

上面查询的结果集显示了哪个值在列中重复了多少次。在上面的示例中，“Gaurav”在“name”列中重复两次。可以从下面的‘SELECT *’ 查询中验证同样的情况 -

mysql> Select * from Student;

+------+---------+---------+-----------+
| Id   | Name    | Address | Subject   |
+------+---------+---------+-----------+
| 1    | Gaurav  | Delhi   | Computers |
| 2    | Aarav   | Mumbai  | History   |
| 15   | Harshit | Delhi   | Commerce  |
| 20   | Gaurav  | Jaipur  | Computers |
+------+---------+---------+-----------+

4 rows in set (0.00 sec)

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