Question

我正在尝试生成一个输出，其中仅显示具有Surname =“Berry”课程的人员，其中日期按升序排列。

SELECT c.booking_number AS "Reference",
       c.ldate          AS "Lesson Date",
       s.first_name     AS "Instructor First Name",
       s.surname        AS "Instructor Last Name"
FROM   am_lessons c
       join am_staff s
         ON ( c.staff_id = c.staff_id )
       join am_bookings m
         ON ( c.booking_number = m.booking_number )
       join am_customers f
         ON ( f.customer_id = c.customer_id )
WHERE  f.surname = 'Berry'
ORDER  BY c.ldate ASC

该声明会运行，但会重复出现“预订号码”，“名字”和“第二名”。

Answer 1

首先，您有一些额外/不正确的连接：

SELECT c.booking_number AS "Reference",
       c.ldate          AS "Lesson Date",
       s.first_name     AS "Instructor First Name",
       s.surname        AS "Instructor Last Name"
FROM   am_lessons c
       join am_staff s
         ON ( c.staff_id = s.staff_id ) -- should be s.Staff_Id
       -- JOIN AM_Bookings m           -- this join is not needed
       -- ON (c.Booking_Number = m.Booking_Number)
       join am_customers f
         ON ( f.customer_id = c.customer_id )
WHERE  f.surname = 'Berry'
ORDER  BY c.ldate ASC

其次，您的表中可能有重复的行。如果是这种情况，请修复数据，或添加DISTINCT修饰符。

注意：AM_Bookings上的联接可能用于过滤掉没有关联的Booking_Number的记录。如果是这种情况，您只需过滤c.Booking_Number IS NOT NULL。

SQL：加入语句

1 个答案: