Question

我看到我可以通过这样的方式加入3个表：

select s.name "Student", c.name "Course"
from student s, bridge b, course c
where b.sid = s.sid and b.cid = c.cid

但似乎我只能从每个表中选择一个列？我需要连接3个表中的多个列，其中sys_visits是主表，其中userID = contrID（sys_users，sys_visits）和clientID = clientID（sys_client，sys_visits）

SELECT pid, clientID, contrID, serviceDate, serviceStart, serviceStop FROM sys_visits
SELECT userGroupID, userID, fname, lname FROM sys_users
SELECT clientID, clientFName, clientLName FROM sys_client ORDER BY clientLName ASC

我尝试了很多变化，似乎无法正确理解语法？

Answer 1

改为使用ANSI SQL-92格式的连接。

SELECT  a.*, b.*, c.*
FROM    sys_users a
        INNER JOIN sys_visits b
            ON a.userID = b.contrlD
        INNER JOIN sys_client c
            ON b.clientID = c.clientID

在查询中使用星号表示您正在从表中选择所有列。如果只想选择特定列，请在查询中明确声明列名称，例如：

SELECT  a.userGroupID, a.userID, a.fname, a.lname,
        b.*, 
        c.*
FROM    sys_users a
        INNER JOIN sys_visits b
            ON a.userID = b.contrlD
        INNER JOIN sys_client c
            ON b.clientID = c.clientID

Answer 2

您可以从表格中选择任意数量的列。

    SELECT sv.pid, sv.clientID, sv.contrID, sv.serviceDate, sv.serviceStart, sv.serviceStop, su.userGroupID, su.userID, su.fname, su.lname, sc.clientFName, sc.clientLName 
    FROM sys_visits sv, sys_users su, sys_client sc 
    ORDER BY sc.clientLName ASC

使用JOINS [推荐]

的另一种方法

SELECT sv.pid, sv.clientID, sv.contrID, sv.serviceDate, sv.serviceStart, sv.serviceStop, su.userGroupID, su.userID, su.fname, su.lname, sc.clientFName, sc.clientLName FROM sys_visits sv
JOIN sys_users su ON su.userID = sv.contrID 
JOIN sys_client sc ON sc.clientID = sv.clientID 
ORDER BY sc.clientLName ASC

Answer 3

想想你是否有三个表，例如

指定，资格，专业化和教师表。如果你想在教师表中加入三个表，其中包含teacher_id，teacher_name，designation_id， qualification_id，specialization_id，status等......

    SELECT 
    t.name as teacher_name,
    d.name as designation_name,
    q.name as qualification_name,
    s.name as specialization_name
       FROM teachers t
    INNER JOIN designation d ON t.designation_id = d.id
    INNER JOIN qualification q ON t.qualification_id = q.id
    INNER JOIN specialization s ON t.specialization_id = s.id
    WHERE t.status = 1;

从3个表中加入多个列

3 个答案: