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(jiǎng)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(gè)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(gè)城市的部門個(gè)數(shù)

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(jiǎng)金的每個(gè)部門的部門名和部門的領(lǐng)導(dǎo)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(gè)工種的工種名和員工的個(gè)數(shù)，并且按員工個(gè)數(shù)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