MySQL中的连接查询(等值连接)

SELECT
  girlname,
  boyname
FROM
  boys,
  girls
WHERE
  girls.boyfriend_id=boys.girlfriend_id;

SELECT
  last_name,
  department_name
FROM
  JDSC,
  SNSC
WHERE
  JDSC.`id`=SNSC.`id`;

#"e.job_id"是为了避免歧义
SELECT
  last_name,
  e.job_id,
  job_title
FROM
  ESC e,
  JOBSC j
WHERE
  e.`job_id`=j.`job_id`;

#员工名:last_name
#部门名:department_name
#奖金率:commissiom_pct
SELECT
  last_name,
  department_name,
  commissiom_pct
FROM
  employees e,
  department d
WHERE
  e.`department_id`=d.`department_id`
AND
  e.`commissiom_pct` IS NOT NULL;

#城市分组表名:city
#部门分组表名:departments
SELECT
  COUNT(*) 个数,
  city
FROM
  departments d,
  locations l
WHERE
  d.`location_id`=l.`location_id`
GROUP BY
  city;

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

SELECT
 last_name,
 department_name,
 city
FROM
 employees e,
 departments d,
 locations l
WHERE
 e.`department_id`=d.`department_id`
AND
 d.`location_id`=l.`location_id`
AND
  city LIKE 's%';