以一對多關系連接 MYSQL 中的兩個表，但僅顯示第二個表中的一個條目

Question

如果我有兩個表，Consumer 和 Appointment，是否有辦法加入它們，以便只顯示最近的約會？ 我能夠用 sql 服務器做到這一點，但 mysql 似乎有點不同。

我原以為要執行此操作的查詢是

SELECT Con.ConsumerID, 
       Con.ConsumerName,
       App.AppointmentID, 
       App.ScheduledDate, 
       App.Location 
FROM Consumer Con 
LEFT JOIN Appointment AS App 
  ON Con.ConsumerID = (SELECT ConsumerID 
                       FROM Appointment AS App2 
                       WHERE App2.ConsumerID = Con.ComsumerID 
                       ORDER BY ScheduledDate 
                       DESC 
                       LIMIT 1)

這似乎返回了所有具有所有約會的消費者，所以我有很多重復的消費者。

我的桌子看起來像

• 消費者

  • 消費者ID
  • 消費者姓名

• 預約

  • 預約ID
  • 消費者ID
  • 約定的日期
  • 地點

Answer 1

使用下面的查詢。

SELECT Consumer.ConsumerName FROM Consumer WHERE Consumer.ConsumerID=(SELECT Appointment.AppointmentID FROM Appointment ORDER BY Appointment.ScheduledDate DESC LIMIT 1)

為了從兩個表中檢索所有數據，您可以在 Appointment 的 select 中進行上述查詢。

SELECT * FROM Appointment where ConsumerID=(SELECT Consumer.ConsumerID FROM Consumer WHERE Consumer.ConsumerID=(SELECT Appointment.AppointmentID FROM Appointment ORDER BY Appointment.ScheduledDate DESC LIMIT 1))

Answer 2

我讓它工作了。 我想多了。

SELECT
                        Con.ConsumerID,
                        Con.ConsumerName
                        App.AppointmentID,
                        App.ScheduledDate,
                        App.Location
                    FROM
                        Consumer Con
                    LEFT JOIN Appointment AS App
                    ON App.AppointmentID = (
                    SELECT AppointmentID
                    FROM Appointment AS App2
                    WHERE App2.ConsumerID = Con.ConsumerID
                    ORDER BY ScheduledDate DESC LIMIT 1);