分享程序员开发的那些事...
更新时间：2023-11-25 21:29:58
以下经过尝试，测试和验证的方法来检查是否存在行.
The following are tried, tested and proven methods to check if a row exists.
(其中一些我自己使用过，或者曾经使用过).
(Some of which I use myself, or have used in the past).
编辑:我在语法上犯了一个先前的错误，我两次使用mysqli_query().请查阅修订版本.
I made an previous error in my syntax where I used mysqli_query() twice. Please consult the revision(s).
即:
if (!mysqli_query($con,$query))，应该简单地读为if (!$query).
旁注: '".$var."'和'$var'都做相同的事情.您可以使用任何一种，两者都是有效的语法.
Side note: Both '".$var."' and '$var' do the same thing. You can use either one, both are valid syntax.
这是两个已编辑的查询:
Here are the two edited queries:
$query = mysqli_query($con, "SELECT * FROM emails WHERE email='".$email."'");
if (!$query)
{
die('Error: ' . mysqli_error($con));
}
if(mysqli_num_rows($query) > 0){
echo "email already exists";
}else{
// do something
}
以及您的情况:
$query = mysqli_query($dbl, "SELECT * FROM `tblUser` WHERE email='".$email."'");
if (!$query)
{
die('Error: ' . mysqli_error($dbl));
}
if(mysqli_num_rows($query) > 0){
echo "email already exists";
}else{
// do something
}
您还可以将 mysqli_与预准备的语句一起使用方法:
You can also use mysqli_ with a prepared statement method:
$query = "SELECT `email` FROM `tblUser` WHERE email=?";
if ($stmt = $dbl->prepare($query)){
$stmt->bind_param("s", $email);
if($stmt->execute()){
$stmt->store_result();
$email_check= "";
$stmt->bind_result($email_check);
$stmt->fetch();
if ($stmt->num_rows == 1){
echo "That Email already exists.";
exit;
}
}
}
<?php
$email = $_POST['email'];
$mysql_hostname = 'xxx';
$mysql_username = 'xxx';
$mysql_password = 'xxx';
$mysql_dbname = 'xxx';
try {
$conn= new PDO("mysql:host=$mysql_hostname;dbname=$mysql_dbname", $mysql_username, $mysql_password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
exit( $e->getMessage() );
}
// assuming a named submit button
if(isset($_POST['submit']))
{
try {
$stmt = $conn->prepare('SELECT `email` FROM `tblUser` WHERE email = ?');
$stmt->bindParam(1, $_POST['email']);
$stmt->execute();
while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
}
}
catch(PDOException $e) {
echo 'ERROR: ' . $e->getMessage();
}
if($stmt->rowCount() > 0){
echo "The record exists!";
} else {
echo "The record is non-existant.";
}
}
?>
N.B.:
在处理上面使用/概述的表单和POST数组时，请确保POST数组包含值，表单使用POST方法并为输入匹配命名属性.
When dealing with forms and POST arrays as used/outlined above, make sure that the POST arrays contain values, that a POST method is used for the form and matching named attributes for the inputs.
注意:<input type = "text" name = "var">-$_POST['var']匹配. $_POST['Var']没有匹配项.
Note: <input type = "text" name = "var"> - $_POST['var'] match. $_POST['Var'] no match.
咨询:
检查引用时出错:
请注意，如果您正在访问此问答，并且您正在使用mysql_进行连接(并进行查询)，则MySQL API不会混在一起.
Please note that MySQL APIs do not intermix, in case you may be visiting this Q&A and you're using mysql_ to connect with (and querying with).
请咨询以下内容:
如果您使用的是mysql_ API，但别无选择，请查阅以下有关堆栈的Q& A:
If you are using the mysql_ API and have no choice to work with it, then consult the following Q&A on Stack:
不推荐使用mysql_*函数，这些函数将从将来的PHP版本中删除.
The mysql_* functions are deprecated and will be removed from future PHP releases.
您还可以向(a)行添加UNIQUE约束.
参考文献: