SQL查詢工作有時

Question

我有這個疑問，它似乎工作的大部分時間，但我仍然得到它空值，當我知道它應該返回的東西，

我開始select，那麼這個

(select sum(total) from orders 
     where customer = 9 
     and iscredit = 1 
     and isdeleted = false and not id = 1560) 

代碼的這種安寧使我獲得了客戶9的訂單總量，而不是當前訂單，就像以前的訂單總額一樣...也注意到iscredit = 1意味着這些是信用訂單。

接下來，我要添加這個查詢

(select sum(total) from orders 
     where customer = 9 
     and iscredit = 0 
     and isdeleted = false and not id = 1560) 

做同樣的事情，但iscredit爲0，因此訂單是沒有學分。

接下來我想什麼減去已支付與此查詢

- (select ifnull(sum(p.amount), 0) from payment p 
     inner join orders o 
     on p.order = o.id 
     where o.customer = 9) as previous 

因此，所有這一起我什麼查詢看起來像....

select 
(
    select sum(total) 
    from orders 
    where customer = 9 and iscredit = 1 and isdeleted = false and not id = 1560 
) 
+ 
(
    select sum(total) 
    from orders 
    where customer = 9 and iscredit = 0 and isdeleted = false and not id = 1560 
) 
- 
(
    select ifnull(sum(p.amount), 0) 
    from payment p 
     inner join orders o 
      on p.order = o.id 
    where o.customer = 9 
) as previous 

有沒有更好的方式來寫這個？

任何提示將不勝感激。

謝謝

Answer 1

這樣的事情會把頭兩個總數合在一起。

(select sum(total) 
from orders 
where customer = 0 
and (iscredit = 1 or iscredit = 0) 
and isdeleted = false 
and not id = 1560) 

這將返回null對於沒有匹配行，所以你可能要添加：

(select ifnull(sum(total), 0) 
from orders 
where customer = 0 
and (iscredit = 1 or iscredit = 0) 
and isdeleted = false 
and not id = 1560) 

這可能是你的問題的根源。