MySQL 如何使用MySQL查找重复行并在单独的列中显示它们的计数

为此，使用GROUP BY HAVING子句。让我们首先创建一个表 –

mysql> create table DemoTable(
   Name varchar(100),
   Age int
);
Query OK, 0 rows affected (1.50 sec)

使用插入命令将一些记录插入表中 –

mysql> insert into DemoTable values('Chris',23);
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable values('David',21);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values('Chris',23);
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values('Chris',21);
Query OK, 1 row affected (0.27 sec)
mysql> insert into DemoTable values('Mike',25);
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values('David',21);
Query OK, 1 row affected (0.10 sec)

使用select语句显示表中的所有记录 –

mysql> select *from DemoTable;

这将产生以下输出 –

+-------+------+
| Name  | Age  |
+-------+------+
| Chris | 23   |
| David | 21   |
| Chris | 23   |
| Chris | 21   |
| Mike  | 25   |
| David | 21   |
+-------+------+
6 rows in set (0.00 sec)

以下是查找重复行并在单独的列中显示计数的查询语句 –

mysql> select Name,Age,count(*) AS Repeated from DemoTable
group by Name,Age
having Repeated > 1;

这将产生以下输出 –

+-------+------+----------+
| Name  | Age  | Repeated |
+-------+------+----------+
| Chris | 23   | 2        |
| David | 21   | 2        |
+-------+------+----------+
2 rows in set (0.00 sec)

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