convert value from routes/uri to string

I don't see why you are using the sub-select. Here is how to do the above using Query Builder, but without the sub-select.

PHP Code:

   public function user_campaign($key, $value)
    {
        return $this->db
            ->where($key, $value)
            ->join('campaigns', 'users_campaigns.id = campaigns.id', 'inner')
            ->get('users')
            ->row();
    } 


I think in basic queries it is required to select in sub-queries, am I correct?

I have used the logic above before but with basic queries that are required to use sub-select so that it gets erorr which is caused to clash in the ID column, that's why I rotate that logic.


the above method does produce the data that I want. but the method above is not a sub-query.
the concern is that in the future I have to use multiple sub-queries.

what if I faced a query like this (this is only for example):

PHP Code:

public function user_campaign($var1, $var2, $var3, $var4 )
{
    return $this->db->query("
        SELECT *
        FROM (
            SELECT *
            FROM users
            WHERE $var1 = '$var2'
        ) a
        INNER JOIN (
            SELECT *
            FROM campaigns
            WHERE $var3 = '$var3'
        ) b
        ON a.id = b.id
    ")->row();
} 


I apologize in advance if I bother you