Question

我试图运行查询我phpmyAdmin如下

SELECT
  orders_history.id,
  orders_history.`items`,
  orders_history.`transaction_id`,
  orders_history.`quantity`,
  estockClaims.`esquantity`,
  IFNULL( esquantity, 0 ),
  orders_history.`quantity` - estockClaims.`esquantity` AS myquantity
FROM orders_history
LEFT JOIN estockClaims
  ON orders_history.transaction_id = estockClaims.transaction_id
 AND orders_history.items = estockClaims.items
LIMIT 0 , 100

它给了我这个结果：

       ----------------------------------------------------------------------
       id     items      transaction_id    quantity   esquantity   IFNULL(esquantity , 0 )   myquantity
       1      FR               001           100        NULL              0                        NULL
       2      BR               002            10        NULL              0                        NULL
       3      WR               003            25        25               25                        0
       4      CR               004            50        3                 3                        47

如何解决这个问题，以便NULL不是NULL，而是更改为0.提前感谢。

由于

Answer 1

您已在下一栏中找到它。您需要做的是删除原始esquantity列并为IFNULL...列创建别名，如下所示：

SELECT orders_history.id, orders_history.`items` , orders_history.`transaction_id` , 
       orders_history.`quantity` , IFNULL( esquantity, 0 ) AS esquantity, 
       orders_history.`quantity` - estockClaims.`esquantity` AS myquantity
FROM orders_history
LEFT JOIN estockClaims ON orders_history.transaction_id = estockClaims.transaction_id
AND orders_history.items = estockClaims.items
LIMIT 0 , 100

我提到的改变在上面第2行。

更新

获得

orders_history.`quantity` - estockClaims.`esquantity` AS myquantity

要显示预期结果，您需要＆＃34; unnullify＆＃34;再次esquantity字段，以便减法可行：

orders_history.`quantity` - IFNULL( estockClaims.`esquantity`, 0 ) AS myquantity

这将确保您不再获得，例如：

100 - NULL

但请改为：

100 - 0

将返回正确的值。

如果esquantity为NULL并且只使用quantity的值，您也可以跳过整个减法事项。

Answer 2

您可以使用IF查看esquantity和myquantity列：

IF(esquantity IS NULL, 0, esquantity)

和

IF(myquantityIS NULL, 0, myquantity)

或使用IFNULL作为DanFromGermany说

Answer 3

原因是您使用它作为选择而不是在进行减法时。使用方法如下：

SELECT orders_history.id, orders_history.`items` , orders_history.`transaction_id` ,          orders_history.`quantity` , orders_history.`quantity` - IFNULL( esquantity, 0 ) AS myquantity
FROM orders_history
LEFT JOIN estockClaims ON orders_history.transaction_id = estockClaims.transaction_id
AND orders_history.items = estockClaims.items
LIMIT 0 , 100

Answer 4

select temp.id, items, transaction_id, quantity, ifNULL(esquantity, 0), ifNULL(myquantity, 0)
from (SELECT
  orders_history.id,
  orders_history.`items`,
  orders_history.`transaction_id`,
  orders_history.`quantity`,
  estockClaims.`esquantity`
  orders_history.`quantity` - estockClaims.`esquantity` AS myquantity
FROM orders_history
LEFT JOIN estockClaims
  ON orders_history.transaction_id = estockClaims.transaction_id
 AND orders_history.items = estockClaims.items
LIMIT 0 , 100) temp

Answer 5

您还可以使用 COALESCE 将 NULL值替换为0

检查此查询。

SELECT orders_history.id, orders_history.`items` , orders_history.`transaction_id` , 
       orders_history.`quantity` , COALESCE( esquantity, 0 ) AS esquantity, 
       orders_history.`quantity` - COALESCE(estockClaims.`esquantity`, 0) AS myquantity
FROM orders_history
LEFT JOIN estockClaims ON orders_history.transaction_id = estockClaims.transaction_id
AND orders_history.items = estockClaims.items
LIMIT 0 , 100

将Null改为0

5 个答案: