MySQL（8） 之 DQL查询（分组查询）

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分组查询

# 语法
/*
select 分组函数，列
from 表
【where 筛选条件】
group by 分组的类表
【order by 子句】

*/
# 查询每个工种的最高工资
SELECT MAX(salary),job_id 
FROM employees
GROUP BY job_id;

# 查询邮箱中包含c，每个部门的平均工资；
SELECT AVG(salary),department_id
FROM employees
WHERE email LIKE "%c%"
GROUP BY department_id;

# 查询有奖金的每个领导手下员工的最高工资；
SELECT MAX(salary),manager_id 
FROM employees
WHERE commission_pct IS NULL
GROUP BY manager_id;

# 查询那个部分员工的个数大于2
SELECT COUNT(*),department_id
FROM employees
GROUP BY department_id
HAVING COUNT(*)>2;

#查询每个工种有奖金的员工的最高工资>12000的工种编号和最高工资；
SELECT job_id ,MAX(salary)
FROM employees
WHERE commission_pct IS NULL
GROUP BY job_id
HAVING MAX(salary)>12000;

# 查询领导编号>102 的每个领导手下的最低工资>5000的领导编号是那个；
# 以及其最低工资；
SELECT manager_id ,MIN(salary)
FROM employees
WHERE manager_id >102
GROUP BY manager_id
HAVING MIN(salary)>5000;

# 按员工姓名的长度分组，查询每一组的员工个数，筛选员工个数>5的有哪些
SELECT COUNT(*) c,LENGTH(last_name) len_name
FROM employees
GROUP BY len_name
HAVING c>5

# 多个字段分组查询

# 查询每个部门中每个工种的平均工资
SELECT department_id,job_id ,AVG(salary)
FROM employees
GROUP BY department_id ,job_id;

# 查询每个部门中每个工种的平均工资,并且按升序排序
SELECT department_id,job_id ,AVG(salary)
FROM employees
GROUP BY department_id ,job_id
ORDER BY AVG(salary);