What am I doing wrong in this query?

Question

There are three tables,

• storing user details
• storing groups details
• storing user and group ids.

I need to check if a user is already a member of one group. I'm using this query to achieve that:

SELECT u.id, g.id 
FROM users u, groups g 
INNER JOIN user_groups ug 
ON ug.user_id = u.id AND ug.group_id = g.id 
WHERE ug.user_id = ? AND ug.group_id = ?

but this is throwing me an error:

Call to a member function bind_param() on boolean in

I have checked if i have misspelled some word in my query and everything is okay.

EDIT:

Here is a function:

public function isUserMember($user_id, $group_id) {
        $stmt = $this->conn->prepare("
            SELECT u.id, g.id from users u, groups g 
            INNER JOIN user_groups ug 
            ON ug.user_id = u.id AND ug.group_id = g.id 
            WHERE ug.user_id = ? AND ug.group_id = ?");
        $stmt->bind_param("ii", $user_id, $group_id); // here i'm getting an error
        $stmt->execute();
        $stmt->store_result();
        $num_rows = $stmt->num_rows;
        $stmt->close();
        return $num_rows > 0;
}

Answer 1

Try following changes

removed unnecessary join with user table because if you have user_id and group_id you don't need to join it with user

SELECT ug.id, g.id 
from  user_groups ug  
inner join  groups g 
on ug.group_id = g.id 
WHERE ug.user_id = ? AND ug.group_id = ?

Answer 2

Your specific issue Error statement is:

Call to a member function bind_param() on boolean in

at:

 $stmt->bind_param("ii", $user_id, $group_id); 

What this means is that there is no function bind_param() on boolean (true or false) , so this means your $stmt is a boolean, meaning the statement defining line has returned FALSE .

so:

 $stmt = $this->conn->prepare(" SELECT u.id, g.id from users u, groups g INNER JOIN user_groups ug ON ug.user_id = u.id AND ug.group_id = g.id WHERE ug.user_id = ? AND ug.group_id = ?"); 

This is where the problem is. Others in comments have stated that your SQL query is incorrect, which would result in a boolean fail, however, if it is not your SQL query itself that is failing, then you would need to establish that the $this->conn value has been successfully generated and that it is a valid object entity.

Try to output an error log something like:

 if(!$stmt = $this->conn->prepare($sql)){
            $errorDump = '
            Error 1 '.date("r").' :
            ';
            $errorDump .= $this->conn->error;
            $errorDump .= "\n\nBacktrace:\n".print_r(debug_backtrace(),TRUE);
            $errorDump .= "
             SQL: ".$sql;
            error_log($errorDump);
            unset($errorDump);
            return false;
        }
    ....
   //carry on with the query as it's ok 

The above is a bit quick and dirty but when your $stmt returns false this error report will tell you why. You can then use that error information to solve your Query or your PHP variable structure.