語(yǔ)法:
select 分組函數(shù)，列（要求出現(xiàn)在group by的后面）
from 表
where ..
group by 分組的列表
order by ...

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#案例：查詢各個(gè)部門的平均工資

SELECT AVG(salary),department_id
FROM employees
GROUP BY
    department_id
ORDER BY
    department_id DESC;

#案例:查詢每個(gè)工種的最高工資

SELECT
    MAX(salary),job_id
FROM
    employees
GROUP BY
    job_id;

#案例:查詢每個(gè)部門的位置個(gè)數(shù)

SELECT
    COUNT(location_id),department_name
FROM
    departments
GROUP BY
    department_name;

#案例:查詢郵箱中包含a字符的，每個(gè)部門的平均工資

SELECT
    AVG(salary),department_id
FROM
    employees
WHERE
    email LIKE('%a%')
GROUP BY
    department_id;

#案例：查詢有獎(jiǎng)金的每個(gè)領(lǐng)導(dǎo)手下員工的最高工資

SELECT
    MAX(salary),manager_id
FROM 
    employees
WHERE
    commission_pct IS NOT NULL
GROUP BY 
    manager_id;