mysql 等值連接案例之添加篩選、分組、排序、多表

加篩選

#案例:有獎金的員工名和部門名

SELECT 
    last_name,department_name
FROM
    employees AS e,departments AS d
WHERE
    e.department_id=d.department_id
AND
    e.commission_pct IS NOT NULL;

#案例：查詢城市名中第二個字符為o的部門名和城市名

SELECT
    department_name,city
FROM
    departments AS d,locations AS l
WHERE
    d.location_id=l.location_id
AND
    l.city LIKE'_o%';

加分組

#案例:查詢每個城市的部門個數

SELECT
    COUNT(*),city
FROM
    departments AS d,locations AS l
WHERE
    d.`location_id`=l.`location_id`
GROUP BY
    city;

#案例：查詢有獎金的每個部門的部門名和部門的領導編號和該部門的最低工資

SELECT
    department_name,d.manager_id,MIN(salary)
FROM
    employees AS e,departments AS d
WHERE
    d.department_id=e.department_id
AND
    commission_pct IS NOT NULL
GROUP BY
    department_name,d.manager_id;

加排序
#案例:查詢每個工種的工種名和員工的個數，并且按員工個數降序

SELECT
    job_title,COUNT(*)
FROM
    employees AS e,jobs AS j
WHERE
    e.job_id=j.job_id
GROUP BY
    job_title
ORDER BY
    COUNT(*) DESC;

三表連接
#案例：查詢員工名 、部門名、所在的城市

SELECT
    last_name,department_name,city
FROM
    employees AS e,departments AS d,locations AS l
WHERE
    e.department_id=d.`department_id`
AND
    d.`location_id`=l.location_id