合併兩個SQL SELECT語句返回來自兩個不同表的值

Question

我將如何合併以下兩個sql select語句？

//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

用途：

//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

兩個做它（只是在SQL語句組成部分）的方式：

解決方案1：UNION

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

兩個表基本上都需要相同字段，否則調整聲明的部分SELECT *。

解決方案2：將錶鏈接到

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

首先，我寧願（1），因爲（2）可能是由表設計的影響。