MySQL複雜的SQL查詢顯示空列值，其中表列不匹配

Question

我有兩個表在我的數據庫中：en_page和mwpage。兩個列都有page_title列。我想要的是選擇兩個page_title值匹配的數據。

例如

SELECT EN.page_title ENP, MW.page_title MWP 
FROM en_page AS EN, mwpage AS MW 
WHERE EN.page_title = 'Main_Page' 
AND MW.page_title = 'Main_Page' 
LIMIT 0 , 30 

此查詢工作正常，並返回以下數據：

ENP |  MWP 
Main_Page| Main_Page 

但我有一種特殊情況。如果table.page_title值中的任何一個與條件不匹配，則查詢不會返回任何結果集。我希望它仍然返回結果集凡不匹配的表應該是空的，像下面這樣：

ENP |  MWP 
Main_Page| 

我不知道如何做到這一點。誰能幫忙？

Answer 1

試試這個

SELECT EN.page_title ENP, MW.page_title MWP 
FROM 
    en_page AS EN 
    LEFT OUTER JOIN mwpage AS MW ON EN.page_title = MW.page_title 
WHERE EN.page_title = 'Main_Page' 
LIMIT 0 , 30 

Answer 2

SELECT EN.page_title ENP, MW.page_title MWP 
FROM en_page AS EN, mwpage AS MW 
WHERE (EN.page_title = 'Main_Page' OR EN.page_title='') 
AND (MW.page_title = 'Main_Page' OR MW.page_title = '')  
LIMIT 0 , 30 

Answer 3

爲了處理NULL情況下，只需使用一個CASE WHEN

SELECT EN.page_title ENP, CASE WHEN MW.page_title IS NULL THEN '' ELSE MW.page_title END MWP 
FROM 
    en_page AS EN 
    LEFT OUTER JOIN mwpage AS MW ON EN.page_title = MW.page_title 
WHERE EN.page_title = 'Main_Page' 
LIMIT 0 , 30