MySQL 查询按名称分组并在新列中显示计数
mysqlmysqli database
使用 GROUP BY 和 COUNT() 方法。使用 GROUP BY 对名称进行分组，并使用 COUNT() 方法进行计数。让我们首先创建一个表 −
mysql> create table DemoTable ( Name varchar(30) ); Query OK, 0 rows affected (0.63 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable values('Chris');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable values('Robert');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('Mike');
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable values('Robert');
Query OK, 1 row affected (0.07 sec)
mysql> insert into DemoTable values('Mike');
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable values('David');
Query OK, 1 row affected (0.12 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 | +--------+ | Chris | | Robert | | Mike | | Robert | | Mike | | David | +--------+ 6 rows in set (0.00 sec)
以下是按名称分组并显示计数的查询 −
mysql> select Name,count(Name) as NumberOfRowsPerName from DemoTable group by Name;
这将产生以下输出 −
+--------+---------------------+ | Name | NumberOfRowsPerName | +--------+---------------------+ | Chris | 1 | | Robert | 2 | | Mike | 2 | | David | 1 | +--------+---------------------+ 4 rows in set (0.00 sec)
