如果在SQL的WHERE CLAUSE中找不到某個值，則顯示NULL

Question

我試圖根據它們的列和WHERE IN子句加入兩個表。

SELECT DISTINCT 
    t1.document_num, t2.file_name 
FROM 
    infocard_1 AS t1 
INNER JOIN 
    web_pub_subfile AS t2 on t1.info_card_id = t2.info_card_id 
WHERE 
    lower(t1.vault_name) LIKE N'%su-spec-release%' AND 
    t2.file_name = 
     CASE 
      WHEN t2.file_name IN ('00350.dwg', '00924.dwg', '00960.dwg', '00973.dwg') 
      THEN t2.file_name 
      ELSE NULL 
     END 

我得到的輸出以這種格式

document_num file_name 
------------------------- 
SU-SH3A081  00960.DWG 
SU-SH3A148  00973.DWG 

但我想獲得

document_num file_name 
------------------------- 
null   00350.dwg 
null   00924.dwg 
SU-SH3A081  00960.DWG 
SU-SH3A148  00973.DWG 

有沒有什麼辦法可以做到這一點？請幫幫我。

Answer 1

試試這個：

SELECT distinct t1.document_num,t2.file_name 
FROM web_pub_subfile AS t2 
LEFT JOIN infocard_1 AS t1 on t1.info_card_id = t2.info_card_id AND 
           lower(t1.vault_name) LIKE N'%su-spec-release%' 
WHERE t2.file_name IN ('00350.dwg','00924.dwg','00960.dwg','00973.dwg') 

Answer 2

你需要的是RIGHT JOIN而不是INNER JOIN。詳細瞭解JOINShere的類型。

Answer 3

爲什麼你有一個WHERE表達CASE？這使得它很難閱讀。必要時使用AND或OR和括號來構建您的WHERE子句。你子句的語句：

WHERE lower(t1.vault_name) LIKE N'%su-spec-release%' 
AND t2.file_name IN ('00350.dwg','00924.dwg','00960.dwg','00973.dwg') 

要想從表中的記錄，即使他們沒有在其他表中的比賽，你會外加入其他表。

SELECT DISTINCT ic.document_num, wps.file_name 
FROM web_pub_subfile wps 
LEFT JOIN infocard_1 ic ON ic.info_card_id = wps.info_card_id 
         AND lower(ic.vault_name) LIKE N'%su-spec-release%' 
WHERE wps.file_name IN ('00350.dwg','00924.dwg','00960.dwg','00973.dwg'); 

我用一些可讀的替換你的別名。