涉及多個表和一個OR語句的Mysql查詢

Question

對不起，一個模棱兩可的標題，但我想不出一個好的。

我有2個表：

bookings(booking_id, customer_id) 
charges(customer_id, booking_id, amount) 

凡在收費表中，無論是booking_id或CUSTOMER_ID必須輸入。不是都。

我試圖讓量與某個相關CUSTOMER_ID

因爲CUSTOMER_ID的有時是空的收費表，我必須使用booking_id通過預訂表，獲取CUSTOMER_ID。

所以，我有這樣的查詢：

SELECT c.amount 
FROM charges as c, bookings as b 
WHERE (c.customer_id = 1234) OR 
(c.customer_id = null AND c.booking_id = b.booking_id AND b.customer_id = 1234) 

然而，這似乎創造一個無限循環。

有什麼建議嗎？

感謝，

Answer 1

的問題是，你正在做一個cross join（笛卡爾乘積），根據您的where條款的結構。

更好的方法是使用left outer join（以及正確的連接語法）。因此，如果存在，請加入bookings表。然後使用or的where子句中尋找對customer_id比賽在兩個地方：

SELECT c.amount 
FROM charges as c left outer join 
    bookings as b 
    on c.booking_id = b.booking_id 
WHERE (c.customer_id = 1234) OR (b.customer_id = 1234) 

Answer 2

爲什麼你不使用JOIN？像

SELECT c.amout 
FROM charges AS c 
LEFT JOIN bookings AS b ON c.bookin_id = b.booking_id 
WHERE c.customer_id = 1234 OR b.customer_id = 1234 

Answer 3

SELECT amount, customer_id from charges where customer_id = 1234 
UNION 
select amount, b.customer_id from charges c, bookings b where b.booking_id = c.booking_id and c.customer_id is null and b.customer_id = 1234