Warning mysql_num_rows(): supplied argument is not a valid MySQL result

Question

Why i have this error and how to fix this, I've double checked everything and all is okay

: mysql_num_rows(): supplied argument is not a valid MySQL result resource in on line ：mysql_num_rows（）：第行上提供的参数不是有效的MySQL结果资源
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'like WHERE postID='81' AND userIP='2x2.2x0.x5.xxx'' at line 1

Here is sql

$ip_sql = mysql_query("SELECT userIP FROM like WHERE postID='$id' AND userIP='$ip'");
$count = mysql_num_rows($ip_sql) or die(mysql_error());
if($count==0)
{...

Answer 1

LIKE是保留字-请将其转义

$ip_sql = mysql_query("SELECT userIP FROM `like` WHERE postID='$id' AND userIP='$ip'");

Answer 2

LIKE是SQL中的关键字，使用´

SELECT userIP FROM `like` WHERE postID='$id' AND userIP='$ip

Answer 3

Try connecting first. Are you looking for the null case? If so you have to search a certain row not $count as a whole.

$conn = mysql_connect("localhost", "user", "pass");
$ip_sql = mysql_query("SELECT userIP FROM like WHERE postID='$id' AND userIP='$ip'",$conn);
$count = mysql_num_rows($ip_sql) or die(mysql_error());
if ($count['postID'}==""){
}