selecting a colum from joined tabels in database Codeigniter - php

Question

I am trying to select column name level_name from table levels,
which contains level_id and level_name,
for a user to know what is their level,
The table of users named as users and contain a level_id and user_id,
but I get this error ->
Column 'level_id' in on clause is ambiguous
SELECT `level_name`
FROM `levels`
JOIN `users` ON `level_id` = `level_id` WHERE `user_id` = '9'
here it is the code in the model
public function level_ownprofile($user_id)
{
$this->db->select('level_name');
$this->db->from('levels');
$this->db->join('users', 'level_id = level_id');
$this->db->where('user_id', $user_id);
$query = $this->db->get();
return $query;
}
thanks in advance :)

Answer 1

Change the query to
SELECT `level_name`
FROM `levels` l
JOIN `users` u ON `u`.`level_id` = `l`.`level_id`
WHERE `user_id` = '9'
if you like the table name aliasing method, it is shorter and easier to read.
Or
SELECT `level_name`
FROM `levels`
JOIN `users` ON `users`.`level_id` = `levels`.`level_id`
WHERE `user_id` = '9'
If you prefere to use the full table name everywhere.
Because both tables contain a column with the name level_id the query analyser need to know which one you are addressing.
In codeigniter try
public function level_ownprofile($user_id)
{
$this->db->select('level_name');
$this->db->from('levels l');
$this->db->join('users u', 'u.level_id = l.level_id');
$this->db->where('user_id', $user_id);
$query = $this->db->get();
return $query;
}

Answer 2

Select l.level_name
FROM levels l
JOIN users u
ON u.level_id = l.level_id
and u.user_id = '9'
public function level_ownprofile($user_id)
{
$this->db->select('level_name');
$this->db->from('levels');
$this->db->join('users', 'levels.level_id = users.level_id');
$this->db->where('user_id', $user_id);
$query = $this->db->get();
return $query;
}

Answer 3

public function level_ownprofile($user_id)
{
$this->db->select('l.level_name');
$this->db->from('levels as l');
$this->db->join('users as u', 'l.level_id = u.level_id');
$this->db->where('l.user_id', $user_id);
$query = $this->db->get();
return $query->results();
}