如何在WHERE中使用if語句在php中編寫SQL查詢

Question

如何在查詢的WHERE部分中使用if語句編寫SQL查詢？

這是我的SQL：

$sql = 'SELECT First, Second, 
           Third,Fifth, Status, Isik_id, Comments, Code
    FROM Persons WHERE  Status = 1 && Third = "'.$whoislogged.'" ORDER BY RAND()  LIMIT 1';

Third = "'.$whoislogged.'"是來自會話的詞。

如果$ whoislogged存在並且等於Third，則查詢應類似於：

$sql = 'SELECT First, Second, Third,Fifth, Status, Isik_id, Comments, Code
        FROM Persons 
WHERE  Status = 1 && Third = "'.$whoislogged.'" ORDER BY RAND()  LIMIT 1';

但是，如果出現$ whoislogged劑量，則查詢應類似於：

 $sql = 'SELECT First, Second, 
           Third,Fifth, Status, Isik_id, Comments, Code
    FROM Persons WHERE  Status = 1 ORDER BY RAND()  LIMIT 1';

那么如何將所有這些整合到一個查詢中呢？

Answer 1

只需創建一個包含Third語句的新變量

if ( !empty($whoislogged) ) $third = "AND Third = ". $whoislogged;
else $third = "";

$sql = 'SELECT First, Second, 
           Third,Fifth, Status, Isik_id, Comments, Code
    FROM Persons WHERE  Status = 1 '. $third .' ORDER BY RAND()  LIMIT 1';

這不是最有效的方法，但是可以

Answer 2

您可以在查詢本身中處理它。

WHERE  Status = 1 and if(Third = "'.$whoislogged.'", Third = "'.$whoislogged.'" , 1=1)

條件部分將檢查第三個條件是否與$ whoislogged匹配，然后添加id作為條件，否則忽略此條件。