如果字符串不属于某个组然后将另一列留空，该怎么办？

Question

好的，我有2列：购买者 - 订单

如何编写案例陈述以显示：

case when purchaser is blank, then orders is blank

我试过

case when purchaser = ' ' then orders = ' ' else orders end as OrdersEnd

Answer 1

正确的语法如下：

SELECT
    ...
,   CASE WHEN purchaser = '' THEN '' ELSE orders END AS OrdersEnd
FROM ...

请注意＆＃34;购买者是空白的＆＃34;可能意味着＆＃34;是空的或空的＆＃34;。在这种情况下，语法应为

CASE WHEN purchaser is NULL OR purchaser = '' THEN '' ELSE orders END AS OrdersEnd

Answer 2

试试这个：

case when purchaser = '' then '' else orders end as OrdersEnd

Answer 3

＆＃34;空白＆＃34;可能意味着NULL或空格。你没有提到数据库，但以下内容最适用：

(case when purchase is null or replace(purchaser, ' ', '') = '' then ' '
      else orders
 end) as OrdersEnd

Answer 4

您需要检查null和只有空格的购买者。

在购买者无效的情况下，可能还有其他情况......您可以在更多WHEN部分添加这些内容：

SELECT 
  CASE WHEN purchaser is null THEN ''
       WHEN TRIM(purchaser) = '' THEN ''
       ELSE orders END as Orders
FROM table

现在我知道这是MS SQL，这是更短的

SELECT CASE WHEN TRIM(ISNULL(purchaser,'')) = '' THEN '' ELSE orders END AS Orders
FROM table

Answer 5

如果'blank'表示NULL，则可以使用特定于DB的函数。

甲骨文：

SELECT NVL2(purchaser, orders, '') FROM MyTable;

MySQL的：

SELECT IF(purchaser, orders, '') FROM MyTable;