软件测试常用SQL查询语句(一）

一、简单查询

from > distinct > select > order by > limit

(1) 普通查询：select name,age from students;

(2) 起别名查询：select s.name,s.age from students as s;

(3) 分页查询：select name,age from students limit 0，10;

(4)排序查询：select name,age,id from students order by age desc,id asc;

(5)去重查询：select distinct age from students;

二、条件查询

from > where > distinct > select > distinct > order by > limit

eg: select name,age, from students where name=‘xiaoming’ and age=18;

三、高级查询（聚合函数）

sum求和 | avg平均数 | max最大数 | 最小数min
group by | 分组查询

(1) 求班级男女平均年龄分别为多少？
select sex avg(age) from students group by sex;

count(*)记录含空值记录数 | count(列名）不含空记录数

(2) 求班级男女分别为多少人？
select sex count(*) from students group by sex;

(3) 查询每个部门里，每种职位的平均底薪。
select deptno,job,count(*),avg(sal) from t_emp group by deptno,job order by deptno;

group_concat | 可以搭配group by使用，使某个字段连接成字符串

(4) 查询每个部门内底薪超过2000元的人数和员工姓名。
select deptno grouo_concat(ename) count(*) from t_emp where sal>=2000 group by deptno;

having | 跟在group by 后面的条件语句

eg: select sex avg(age) from students group by sex having age in(10,20);