Question

Warning: mysql_query() expects parameter 1 to be string, resource given in D

$username=$_POST['username'];
$title=$_POST['title'];
$contents=$_POST['contents'];
$sql_check=mysql_query("select * from liuyanban where username=$username");
$re_check=mysql_query($sql_check); //执行SQL语句
$row=mysql_fetch_row($re_check);

if($row['username']==$username){
//if(mysql_num_rows($result) != 0){
echo "该用户已存在";
}
else {
$sql="insert into liuyanban(username,title,contents) values('".$username."','".$title."', '".$contents."')";
mysql_query($sql);
}
帮忙看看我这个是怎么回事儿，新手学习，还请大家多多指教

Answer 1

我也经常出现这种情况，都是不注意啊，除了数字都要加引号，应该为$sql_check=mysql_query("select * from liuyanban where username='{$username}'");

Answer 2

mysqli_query()期望参数1是string
检查自己的mysqli_query()方法所传进去的参数是否正确

Answer 3

mysql_query("select * from liuyanban where username=$username");
学习sql基础应该打牢，你现在查询的username字段应该是字符类型的，那么字符字段在查询语句中应该加引号：mysql_query("select * from liuyanban where username=‘$username’");