MySQL高效查询

Question

我是 MySQL 的新手。考虑这张表:

 ID INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  User_name VARCHAR(35) NOT NULL,
  Full_name VARCHAR(55) NOT NULL,
  User_vars VARCHAR(255) NOT NULL,
  BirthDay DATE NOT NULL,
  password CHAR(70) NOT NULL,  
  Security_hint VARCHAR(27) NOT NULL,
  Email VARCHAR(225) NOT NULL,
  userType ENUM ('a','b','c','d') NOT NULL DEFAULT 'a',
  Signup_Date TIMESTAMP NOT NULL  DEFAULT CURRENT_TIMESTAMP,
  activation   TINYINT(1) UNSIGNED NOT NULL,
  Ip BINARY(16) NOT NULL,
  PRIMARY KEY (ID),
  UNIQUE KEY User_name (User_name,Email)

我正在使用以下查询来检查此表中是否存在电子邮件或用户名:

    $query1 ="SELECT id FROM signup WHERE Email='$Email_Input' LIMIT 1";            
$result1 = mysql_query($query1) 

$query2 = "SELECT id FROM signup WHERE User_name='$User_name' LIMIT 1";         
$result2 = mysql_query($query2);

if (mysql_num_rows($result2)>0){    
echo '1';
}
else if (mysql_num_rows($result1)>0){   

echo '1';
}

我的问题:有没有一种有效的方法可以只发出一个查询来检查两者是否存在？

Answer 1

是的，你可以这样做:

SELECT ID FROM signup WHERE Email ='$Email_Input' LIMIT 1
UNION ALL 
SELECT id FROM signup WHERE User_name='$User_name' LIMIT 1

也就是说，如果这是两条不同的记录。如果它是相同的记录，那应该回答这两个条件，只需:

 SELECT ID FROM signup
 WHERE Email ='$Email_Input'
   AND User_name='$User_name' 
 LIMIT 1