软件测试人员常用的SQL语句

一、查询实例

1、select 查询字段 from 表名 where 查询条件

举例说明：

表名：student

表中字段：id,name,age,score,subject,class

表中数据：

(1,"Sheldon",18,99,"Maths", "one"),
(1,"Sheldon",18,90,"Chinese","one"),
(1,"Sheldon",18,85,"English","one"),
(2,"Kim",20,89,"Maths","two"),
(2,"Kim",20,95,"Chinese","two"),
(2,"Kim",20,92,"English","two");

1）查询出某条件下的所有信息

# 查询出表student中age为18的所有学生信息

select * from student where age=18 

2）求和

# 计算并查询出表student中name为Sheldon的学生的总分数

select sum(score) from student where name="Sheldon"   

3）求平均数

# 计算并查询出表student中name为Sheldon的学生的平均分数

select avg(score) from student where name="Sheldon"

4）求最小值：

# 计算并查询出表student中name为Sheldon的学生的最低分数

select min(score) from student where name="Sheldon"

5）求最大值

# 计算并查询出表student中name为Sheldon的学生的最高分数

select max(score) from student where name="Sheldon"

6）对查询结果排列

#查询出表student中name为Sheldon的学生的信息，且按照分数倒序排列（desc是逆序排序，asc是正序排序，asc可省略不写）

select * from student where name="Sheldon" order by score desc

7）求总数（未去重）

# 计算并查询出class为one的班级学生总数（实际上只有一个学生）

select count(*) from student from where class="one"

8）求总数（去重）

# 去重统计出class为one的班级学生总数

select count(distinct id) from student

9）根据一个或多个列表字段进行分组统计查询：

# 统计每个班19岁以上的学生人数（执行顺序where过滤->分组->聚合函数）
select class,count(distinct age) from student where age>19 group by class

表student如下：

10）多表连接查询：

表student如下：

表info如下：

# 两个表连接，并去掉重复的列
select a.*,b.address from student a join info b on a.id=b.id

11）嵌套查询：

# 查询出所有学生的id，name和address
select a.id,a.name,(select b.address from info b where a.id=b.id) address from student a

或者也可以用：

select a.id,a.name,b.address from student a,info b where a.id=b.id

二、插入、修改和删除实例

1.插入：

# 插入多条数据
insert into student values
(1,"Sheldon",18,99,"Maths", "one"),
(1,"Sheldon",18,90,"Chinese","one"),
(1,"Sheldon",18,85,"English","one"),
(2,"Kim",20,89,"Maths","two"),
(2,"Kim",20,95,"Chinese","two"),
(2,"Kim",20,92,"English","two");

2.修改：

# 修改Kim的Maths分数为92
update student set score=92 where name="Kim" and subject="Maths"

3.删除：

# 删除Kim的English信息
delete from student where name="Kim" and subject="English"