为此,将GROUP BY与COUNT(*)一起使用。让我们首先创建一个表-
create table DemoTable
(
EmployeeId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
EmployeeGender varchar(40)
);
使用插入命令在表中插入一些记录-
insert into DemoTable(EmployeeGender) values('MALE');
insert into DemoTable(EmployeeGender) values('FEMALE');
insert into DemoTable(EmployeeGender) values('FEMALE');
insert into DemoTable(EmployeeGender) values('FEMALE');
insert into DemoTable(EmployeeGender) values('MALE');
insert into DemoTable(EmployeeGender) values('MALE');
insert into DemoTable(EmployeeGender) values('MALE');
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-
+------------+----------------+
| EmployeeId | EmployeeGender |
+------------+----------------+
| 1 | MALE |
| 2 | FEMALE |
| 3 | FEMALE |
| 4 | FEMALE |
| 5 | MALE |
| 6 | MALE |
| 7 | MALE |
+------------+----------------+
7 rows in set (0.00 sec)
以下是对varchar列求和的查询。这将对MALE和FEMALE列值求和,并显示计数-
select EmployeeGender,count(*) from DemoTable
group by EmployeeGender;
这将产生以下输出-
+----------------+----------+
| EmployeeGender | count(*) |
+----------------+----------+
| MALE | 4 |
| FEMALE | 3 |
+----------------+----------+
2 rows in set (0.00 sec)