好资源导航 » 文章资讯 » 如何计算MySQL中的非重复列？

如何计算MySQL中的非重复列？

2024-05-18 02:53:04 554

您需要为此使用GROUPBY。让我们首先创建一个表-

create table DemoTable
   (
   StudentFirstName varchar(20)
   );

使用插入命令在表中插入记录-

insert into DemoTable values('John');
insert into DemoTable values('Carol');
insert into DemoTable values('John');
insert into DemoTable values('John');
insert into DemoTable values('Bob');
insert into DemoTable values('David');
insert into DemoTable values('Bob');
insert into DemoTable values('Carol');
insert into DemoTable values('Robert');

使用select语句显示表中的所有记录-

select * from DemoTable;

这将产生以下输出-

+------------------+
| StudentFirstName |
+------------------+
| John             |
| Carol            |
| John             |
| John             |
| Bob              |
| David            |
| Bob              |
| Carol            |
| Robert           |
+------------------+
9 rows in set (0.00 sec)

这是计算MySQL中不同列的查询-

select StudentFirstName,count(*) from DemoTable
group by StudentFirstName;

这将产生以下输出-

+------------------+----------+
| StudentFirstName | count(*) |
+------------------+----------+
| John             | 3        |
| Carol            | 2        |
| Bob              | 2        |
| David            | 1        |
| Robert           | 1        |
+------------------+----------+
5 rows in set (0.00 sec)

返回顶部
3162201930
czq8825@qq.com

如何计算MySQL中的非重复列？

热门推荐

随机推荐