<?php
    $username = $_POST['username'];
    $password = $_POST['password'];
    $result = mysql_query("SELECT * FROM Users WHERE UserName LIKE '".$username."'");

    while($row = mysql_fetch_array($result))
    {
        echo $row['FirstName'];
    }
?>

如果有一个用户具有唯一的用户名，您可以使用“=”表示。没有必要喜欢。

您的查询将是:

mysql_query("SELECT * FROM Users WHERE UserName ='".$username."'");

当数据库连接失败时，通常会出现错误，因此请确保连接数据库或包含数据库文件。

include_once(db_connetc.php');

OR

// Create a connection
$connection = mysql_connect("localhost", "root", "") or die(mysql_error());

//Select database
mysql_select_db("db_name", $connection) or die(mysql_error());

$employee_query = "SELECT * FROM employee WHERE `id` ='".$_POST['id']."'";

$employee_data = mysql_query($employee_query);

if (mysql_num_rows($employee_data) > 0) {

    while ($row = mysql_fetch_array($employee_data)){
        echo $row['emp_name'];
    } // end of while loop
} // end of if

最佳实践是在sqlyog中运行查询，然后将其复制到页面代码中。 始终将查询存储在一个变量中，然后回显该变量。然后传递给mysql_query($query_variable);。

不要使用已废弃的mysql_*函数(在php 5.5中已废弃的将在php 7中被删除)，你可以使用mysqli或pdo来实现

下面是完整的选择查询

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$sql = "SELECT id, firstname, lastname FROM MyGuests";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // output data of each row
    while($row = $result->fetch_assoc()) {
        // code here 
    }
} else {
    echo "0 results";
}
$conn->close();
?>

试试这个

$username = $_POST['username'];
$password = $_POST['password'];
$result = mysqli_query('SELECT * FROM Users WHERE UserName LIKE $username');

if($result){
while($row = mysqli_fetch_array($result))
{
    echo $row['FirstName'];
}
}

如果检查时没有出现任何MySQL错误，请确保正确创建了数据库表。这发生在我身上。寻找任何不需要的逗号或引号。

当查询中出现错误导致查询失败时，将显示此错误消息。它会在使用时显现出来:

mysql_fetch_array / mysqli_fetch_array () 作用是()/ mysqli_fetch_assoc () mysql_num_rows () / mysqli_num_rows ()

注意:如果查询不影响任何行，则不会出现此错误。只有语法无效的查询才会产生此错误。

故障排除步骤

Make sure you have your development server configured to display all errors. You can do this by placing this at the top of your files or in your config file: error_reporting(-1);. If you have any syntax errors this will point them out to you. Use mysql_error(). mysql_error() will report any errors MySQL encountered while performing your query. Sample usage: mysql_connect($host, $username, $password) or die("cannot connect"); mysql_select_db($db_name) or die("cannot select DB"); $sql = "SELECT * FROM table_name"; $result = mysql_query($sql); if (false === $result) { echo mysql_error(); } Run your query from the MySQL command line or a tool like phpMyAdmin. If you have a syntax error in your query this will tell you what it is. Make sure your quotes are correct. A missing quote around the query or a value can cause a query to fail. Make sure you are escaping your values. Quotes in your query can cause a query to fail (and also leave you open to SQL injections). Use mysql_real_escape_string() to escape your input. Make sure you are not mixing mysqli_* and mysql_* functions. They are not the same thing and cannot be used together. (If you're going to choose one or the other stick with mysqli_*. See below for why.)

其他技巧

Mysql_ *函数不应该用于新代码。它们不再被维护，社区已经开始了弃用过程。相反，你应该学习准备语句并使用PDO或MySQLi。如果你不能决定，这篇文章将帮助你选择。如果你想学习，这里有一个很好的PDO教程。