What am I doing wrong in this query? - php

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.