Question

我正在处理问题，无法解决。

我有五个表：

    t_employee = {employee_id_pk, fullname, phone, position, passport}

    t_facility = {facility_id_pk, direction, title}

    t_employee_facility = {emp_fac_id_pk, employee_id_fk, facility_id_fk}  

    this table is @ManyToMany relationship
    between 't_employee' and 't_facility'

    t_transport = {transport_id_pk, type}

    t_trip = {trip_id_pk, trip_code, employee_id_fk, transport_id_fk}

    this table is @ManyToMany relationship between 't_employee' and 't_transport'

我想获得唯一的行我尝试过这样的事情

SELECT
  employee_id, fullname, passport, phone, position, direction, title,
  trip_code
FROM
  t_facility
  INNER JOIN t_employee_facility USING (facility_id)
  INNER JOIN t_employee USING (employee_id)
  INNER JOIN t_trip USING (employee_id)
GROUP BY
  employee_id,
  facility_id,
  trip_code

共有8个uniquie行。但是上面的示例给了我18，当我删除trip_id时我得到了8行，但是在这种情况下，我会为每个employee_id重复trip_code个值。

我只想提取不重复的行。我想我应该使用INNER JOIN来做到这一点，但我不确定。

是否可以联接所有这些表？

谢谢

致谢

Answer 1

可以使用嵌套联接查询来实现，如下所示：

SELECT B.employee_id, employee_id, fullname, passport, phone,
  position,direction, title, trip_code 
FROM (SELECT A.employee_id, employee_id, fullname, passport, phone,
  position,direction, title  
FROM (SELECT employee_id, direction, title FROM t_facility 
       JOIN t_employee_facility 
         ON t_facility.facility_id = t_employee_facility.facility_id
     ) AS A 
     JOIN employee ON A.employee_id = employee.employee_id) AS B 
JOIN t_trip ON B.employee_id = t_trip.employee_id;

Answer 2

INNER JOIN关键字选择在两个表中都应具有匹配的值。例如：

SELECT id_pk,information,about
FROM information
INNER JOIN employe ON information.id_pk= employe.id_employe;

是的，您可以在对每个表进行声明时加入您的表。

Answer 3

如果您只希望各行具有唯一性，但可以，有些员工会显示多个设施或行程，则可以使用DISTINCT关键字。

SELECT DISTINCT
       employee_id,
       fullname,
       passport,
       phone,
       position,
       direction,
       title,
       trip_code
       FROM t_facility
            INNER JOIN t_employee_facility
                       USING (facility_id)
            INNER JOIN t_employee
                       USING (employee_id)
            INNER JOIN t_trip
                       USING (employee_id);

Answer 4

您的问题中还有很多不清楚的地方，无论如何我仍会发布。

首先，我在t_employee子句中看不到表FROM，因此我不确定此查询是否有效。要获取fullname, passport, phone, position的列值，您需要将相关的表t_employee添加到FROM子句中。

我不太确定JOIN语法，可以检查MySQL JOINs语法here。

SELECT
  employee_id, fullname, passport, phone, position, direction, title,
  trip_code
FROM
  t_employee
  INNER JOIN t_facility USING (facility_id)
  INNER JOIN t_employee_facility USING (facility_id)
  INNER JOIN t_employee USING (employee_id)
  INNER JOIN t_trip USING (employee_id)
GROUP BY
  employee_id,
  facility_id,
  trip_code

如果仍然无法解决问题，您可以尝试进行SELECT DISTINCT来获取唯一记录，请参见语法here。

SQL联接五个表

4 个答案: