左連接獲取分鐘日期

Question

我想每個預訂的第一天在我的數據庫。

表BOOKINGS是這樣的：

id | id_client_booking | the_date 

表CLIENT_BOOKINGS是

id | etc | etc 

上 BOOKINGS

每個id_client_booking correponds到CLIENT_BOOKINGS一個id，並且可以有很多的日期。

我想讓每個客戶端預訂的第一次約會。這個選擇只給我所有客戶預訂的第一個日期。我錯過了什麼？

SELECT 
min(the_date) AS start_date, id_client_booking 
FROM `day_bookings`AS db 
LEFT JOIN `client_bookings`AS cb ON db.id_client_booking = cb.id 

也試過：

SELECT 
min(the_date) AS db.start_date, db.id_client_booking 
       ^^    ^^ 
FROM `day_bookings`AS db 
LEFT JOIN `client_bookings`AS cb ON db.id_client_booking = cb.id 

，但給了錯誤：You have an error in your SQL syntax;

Answer 1

你缺少一個GROUP BY，試試這個：

SELECT MIN(the_date) AS start_date, id_client_booking 
FROM `day_bookings`AS db 
LEFT JOIN `client_bookings`AS cb 
ON db.id_client_booking = cb.id 
GROUP BY id_client_booking 

Answer 2

您只能使用AS關鍵字來定義表達式或別名名稱。
你不能用它直接指向一列。因此是語法錯誤。

SELECT 
min(the_date) AS db.start_date, db.id_client_booking 
       ^^    ^^ 
FROM `day_bookings`AS db 
LEFT JOIN `client_bookings`AS cb ON db.id_client_booking = cb.id 

它應該是：

SELECT 
min(the_date) AS 'start_date', db.id_client_booking 
FROM `day_bookings`AS db 
LEFT JOIN `client_bookings`AS cb ON db.id_client_booking = cb.id 

Answer 3

您需要使用GROUP BY聚合函數，使MIN()作品

SELECT min(the_date) AS start_date, id_client_booking 
FROM `day_bookings` AS db 
LEFT JOIN `client_bookings` AS cb 
ON db.id_client_booking = cb.id 
GROUP BY db.id_client_booking