mysql_fetch_array（）/ mysql_fetch_assoc（）/ mysql_fe

查询可能由于各种原因而失败，在这种情况下，mysql_ *和mysqli扩展名都false将从它们各自的查询函数/方法中返回。您需要测试该错误情况并进行相应处理。

mysql_ *扩展名：

注：该mysql_功能已被弃用，并在PHP版本7已被删除。

请先检查一下，$result然后再传递给mysql_fetch_array。您会发现这是false因为查询失败。请参阅mysql_query文档以获取可能的返回值以及有关如何处理它们的建议。

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

if($result === FALSE) { die(mysql_error()); // TODO: better error handling }

while($row = mysql_fetch_array($result)) { echo $row['FirstName']; } mysqli扩展 程序样式：

$username = mysqli_real_escape_string($mysqli, $_POST['username']); $result = mysqli_query($mysqli, "SELECT * FROM Users WHERE UserName LIKE '$username'");

// mysqli_query returns false if something went wrong with the query if($result === FALSE) { yourErrorHandler(mysqli_error($mysqli)); } else { // as of php 5.4 mysqli_result implements Traversable, so you can use it with foreach foreach( $result as $row ) { ... oo风格：

$username = $mysqli->escape_string($_POST['username']); $result = $mysqli->query("SELECT * FROM Users WHERE UserName LIKE '$username'");

if($result === FALSE) { yourErrorHandler($mysqli->error); // or $mysqli->error_list } else { // as of php 5.4 mysqli_result implements Traversable, so you can use it with foreach foreach( $result as $row ) { ... 使用准备好的语句：

$stmt = $mysqli->prepare('SELECT * FROM Users WHERE UserName LIKE ?'); if ( !$stmt ) { yourErrorHandler($mysqli->error); // or $mysqli->error_list } else if ( !$stmt->bind_param('s', $_POST['username']) ) { yourErrorHandler($stmt->error); // or $stmt->error_list } else if ( !$stmt->execute() ) { yourErrorHandler($stmt->error); // or $stmt->error_list } else { $result = $stmt->get_result(); // as of php 5.4 mysqli_result implements Traversable, so you can use it with foreach foreach( $result as $row ) { ...