语法错误，意外 'mysqli_num_rows'

Question

这是我的代码：

$u_check = mysql_query("SELECT username FROM users WHERE usnername='$un' '");
$check = mysqli_num_rows ( $u_check );

我收到以下错误：

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\Socially\index.php on line 27

我无法解决这个问题，我正在使用教程来帮助我做一些事情，这就是他输入的内容。我真的很想修复它，这样我就可以继续我想做的事；我正在做数据库，因为我正在制作登录和注册表单。请帮忙。当我在 phpmyadmin 的 sql 选项卡中键入 $check = mysqli_num_rows ( $u_check ); 时，我收到此消息：

静态分析：

3 errors were found during analysis.
Unexpected character. (near "$" at position 0)
Unexpected character. (near "$" at position 25)
Unexpected beginning of statement. (near "$" at position 0)

SQL query:
$check = mysqli_num_rows($u_check)

MySQL said: Documentation

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use

near '$check = mysqli_num_rows($u_check)' at line 1

Answer 1

您正在混合使用 MySQL 和 MySQLi

如果您正在使用 MySQL:

$u_check = mysql_query("SELECT username FROM users WHERE usnername='$un'");
$check = mysql_num_rows ($u_check);

如果您正在使用 MySQLi:

$u_check = mysql_query($con, "SELECT username FROM users WHERE usnername='$un'");
$check = mysqli_num_rows ($u_check);

（如果您使用 MySQL，请将 $con 替换为您的数据库参数）

也有可能您在查询中指的是 username 而不是 usnername。

Answer 2

替换：

$u_check = mysql_query("SELECT username FROM users WHERE usnername='$un' '");

与：

$u_check = mysqli_query("SELECT username FROM users WHERE usnername = $un");

你总是把变量放在双引号里，否则脚本认为你写的是一个字符串，而不是一个变量。

语法错误，意外 'mysqli_num_rows'

syntax error, unexpected 'mysqli_num_rows'

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