php - 如果第一个查询没有返回结果，则使用第二个查询

Question

我正在制作一个系统，我需要检查第一个表或第二个表中是否存在电子邮件。

    $results = mysqli_query($db,"SELECT * FROM table_1 WHERE email='$email'");
    if(count($results) == 0)
    {
        $results = mysqli_query($db,"SELECT * FROM table_2 WHERE email='$email'");
    }

我想制作一个mysql，这样就不需要两个了。由于两个表结构不同，UNION 并不是没有给出正确的结果。有没有一种没有UNION或JOINS

的方法

我一直在尝试使用 UNION

SELECT * FROM ( SELECT *, 1 as preference FROM table_1 WHERE email = 'doc@demo.com' UNION SELECT *, 2 as preference FROM table_2 WHERE email = 'doc@demo.com' ) T ORDER BY preference LIMIT 1

但问题是，如果表 2 的情况满足，则考虑表 1 的字段，并且所有值都会不匹配

Answer 1

我找到了自己问题的解决方案，所以只是想分享它

SELECT * FROM (
  SELECT email,password,user_role, id as customer_id,id as user_id, 1 as preference 
    FROM table1 WHERE email = 'raj@demo.com'
   UNION 
  SELECT email,password,user_role, customer_id,id, 2 as preference 
    FROM table2 WHERE email = 'doc@demo.com' 
) T ORDER BY preference
LIMIT 1