php - 如何在PHP中使用WHERE中的if语句编写sql查询

Question

如何在查询的 WHERE 部分中编写带有 if 语句的 SQL 查询？

这是我的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.'" 是来自 session 的单词。

如果 $whoislogged 存在并且等于 Third，则查询应如下所示:

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

但是如果 $whoislogged dosent 出现，那么查询应该是这样的:

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

那么我怎样才能将所有这些放入一个查询中呢？

Answer 1

您可以在查询本身中处理它。

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

条件部分将检查第三个是否与 $whoislogged 匹配，如果为 true，则添加 id 作为条件，否则忽略此条件。