php - mysql_num_rows 给出错误 "mysql_num_rows() expects parameter 1 to be resource"

Question

public function doesUserExist($u) {

    $this->dbConnect();

    mysql_select_db($this->database);

    $sUser = mysql_real_escape_string($u);

    $query = "SELECT username FROM $this->table WHERE username='$sUser'";
    $doesFieldExist = false;

    if (mysql_num_rows($query) > 0) {
        $doesFieldExist = true;
    }

    $this->dbDisconnect();

    return $doesFieldExist;

}

我在这一行 (60) 上收到错误

if (mysql_num_rows($query) > 0) {

错误是:

Warning: mysql_num_rows() expects parameter 1 to be resource, string given in C:\Users\Tom\Dropbox\public_html\classes\database.class.php on line 60

对于我正在使用的查询，mysql_num_rows($query) 应该返回 1。我在这里进行了 google 和检查，但看不出我做错了什么。

Answer 1

您还没有真正执行您的查询:

$query = "SELECT username FROM $this->table WHERE username='$sUser'";
$doesFieldExist = false;

// Execute the query with mysql_query()
$result = mysql_query($query);

// $result is a result resource that can be passed 
// to mysql_num_rows() unless the query failed and $result is FALSE
if ($result && mysql_num_rows($result) > 0) {
    $doesFieldExist = true;
}