使用MySQL连接三个表
我有三个表名
**Student Table** ------------- id name ------------- 1 ali 2 ahmed 3 john 4 king **Course Table** ------------- id name ------------- 1 physic 2 maths 3 computer 4 chemistry **Bridge** ------------- sid cid ------------- 1 1 1 2 1 3 1 4 2 1 2 2 3 3 3 4 4 1 4 2 现在要显示他所学习的课程名称，
**Result** --------------------------- Student Course --------------------------- ahmed physic ahmed maths ahmed computer ahmed chemistry ali physic ali maths john computer john chemistry king physic king maths
我build立以下查询
select s.name as Student, c.name as Course from student s, course c join bridge b on c.id = b.cid order by s.name
但它不会返回所需的结果…
如果我想find谁是经理比其他人更常规化的forms是什么：
**employee** ------------------- id name ------------------- 1 ali 2 king 3 mak 4 sam 5 jon **manage** -------------- mid eid -------------- 1 2 1 3 3 4 4 5
并想要得到这个结果：
**result** -------------------- Manager Staff -------------------- ali king ali mak mak sam sam jon
只需使用：
select s.name "Student", c.name "Course" from student s, bridge b, course c where b.sid = s.sid and b.cid = c.cid
使用ANSI语法，它将更加清楚你如何join表格：
SELECT s.name as Student, c.name as Course FROM student s INNER JOIN bridge b ON s.id = b.sid INNER JOIN course c ON b.cid = c.id ORDER BY s.name
为了规范化的forms
select e1.name as 'Manager', e2.name as 'Staff' from employee e1 left join manage m on m.mid = e1.id left join employee e2 on m.eid = e2.id
SELECT * FROM user u JOIN user_clockits uc ON u.user_id=uc.user_id JOIN clockits cl ON cl.clockits_id=uc.clockits_id WHERE user_id = 158
SELECT employees.id, CONCAT(employees.f_name," ",employees.l_name) AS 'Full Name', genders.gender_name AS 'Sex', depts.dept_name AS 'Team Name', pay_grades.pay_grade_name AS 'Band', designations.designation_name AS 'Role' FROM employees LEFT JOIN genders ON employees.gender_id = genders.id LEFT JOIN depts ON employees.dept_id = depts.id LEFT JOIN pay_grades ON employees.pay_grade_id = pay_grades.id LEFT JOIN designations ON employees.designation_id = designations.id ORDER BY employees.id;
你可以像上面这个例子一样join多个表。
用这个：
SELECT s.name AS Student, c.name AS Course FROM student s LEFT JOIN (bridge b CROSS JOIN course c) ON (s.id = b.sid AND b.cid = c.id);
查询join两个以上的表格：
SELECT ops.field_id, ops.option_id, ops.label FROM engine4_user_fields_maps AS map JOIN engine4_user_fields_meta AS meta ON map.`child_id` = meta.field_id JOIN engine4_user_fields_options AS ops ON map.child_id = ops.field_id WHERE map.option_id =39 AND meta.type LIKE 'outcomeresult' LIMIT 0 , 30
