如何使用 MySQL 查找重复行并在单独的列中显示其计数?
mysqlmysqli database更新于 2025/12/25 2:20:17
为此，请使用 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 insert 命令在表中插入一些记录 −
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 −
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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