如何處理字符串不屬於一個組，然後使另一個列空白？

Question

行，所以我有2列：買方 - 訂單

我怎樣寫一個case語句顯示：

case when purchaser is blank, then orders is blank 

我試圖

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

Answer 1

正確的語法如下：

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

請注意，「購買者爲空」可能意味着「爲空或空」。在這種情況下，語法應爲

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

Answer 2

試試這個：

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

Answer 3

「空白」 可能意味着NULL或空格。您沒有提及數據庫，但以下幾項最適用：

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

Answer 4

您需要檢查空值和只有空格的購買者。

可能還有其他的情況下，當購買者無效......你可以添加爲更多的WHEN部分：

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

現在，我知道這是MS SQL，這是短

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

Answer 5

如果'空白'表示NULL，則可以使用特定於DB的功能。

甲骨文：

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

的MySQL：

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