Question

我将如何合并以下两个sql select语句？

//select all rows from our userlogin table where the emails match
$res1 = mysql_query("SELECT * 
                       FROM userlogin 
                      WHERE `email` = '".$email."'");
$num1 = mysql_num_rows($res1);
//if the number of matchs is 1
if($num1 == 1) {
  //the email address supplied is taken so display error message
  echo '<p class="c7">The <b>e-mail</b> address you supplied is already taken. Please go <a href="register.php">back</a> and try again.<br><img src="resources/img/spacer.gif" alt="" width="1" height="15"></p>';
  include_once ("resources/php/footer.php");        
  exit; 
} else {
  //select all rows from our userlogin_fb table where the emails match
  $res2 = mysql_query("SELECT * 
                         FROM userlogin_fb 
                        WHERE `email` = '".$email."'");
  $num2 = mysql_num_rows($res2);
  //if the number of matchs is 1
  if($num2 == 1) {
    //the email address supplied is taken so display error message
    echo '<p class="c7">The <b>e-mail</b> address you supplied is already taken. Please go <a href="register.php">back</a> and try again.<br><img src="resources/img/spacer.gif" alt="" width="1" height="15"></p>';
    include_once ("resources/php/footer.php");      
    exit;   
  } else {;}

Answer 1

使用：

//select all rows from our userlogin table where the emails match
$query = sprintf("SELECT 1 
                    FROM userlogin 
                   WHERE `email` = '%s'
                  UNION ALL
                  SELECT 1
                    FROM userlogin_fb 
                   WHERE `email` = '%s' ",
                   $email, $email);
$res1 = mysql_query($query);
$num1 = mysql_num_rows($res1);
//if the number of matchs is 1
if($num1 >= 1) {
  //the email address supplied is taken so display error message
  echo 'The <b>e-mail</b> address you supplied is already taken. Please go <a href="register.php">back</a> and try again.<br><img src="resources/img/spacer.gif" alt="" width="1" height="15"></p>';
  include_once ("resources/php/footer.php");        
  exit; 
}

Answer 2

两种方法（仅适用于SQL部分）：

解决方案1：UNION

SELECT * 
FROM userlogin 
WHERE email = '$email'
UNION
SELECT * 
FROM userlogin_fb 
WHERE email = '$email';

两个表基本上都需要相同的字段，否则调整SELECT * - 语句的一部分。

解决方案2：链接表

SELECT * 
FROM userlogin AS T1 
JOIN userlogin_fb AS T2 ON T1.email = T2.email
WHERE T1.email = '$email';

首先，我更喜欢（1），因为（2）可能会受到表格设计的影响。

合并两个SQL SELECT语句，返回两个不同表中的值

2 个答案: