Current selection does not contain a unique column. Mysqli. Duplication? - php

Question

I can't seem to select/retrieve the "Package Table" and merge it into 1 table that contains the other table which is "Events Table". I don't know what seems to be the problem though.
Whenever i tried to execute my query and the only thing that pops up is the
events_ table, the Package table on the other hand does not. I tried another another simple query,
SELECT * FROM event_table JOIN package ON event_id WHERE cusact_id = 8 AND event_id=80
And the query works fine.
Event Table (Structure):
http://prntscr.com/gbr6vr
Package Table (Structure):
https://prnt.sc/gbr793
Note: I have a column named package_id on events_table and package. Is that the problem? Im sorry, still new to mysql.
side note:
$c_id = $_SESSION['u_id'];
$n_id = $_GET['n_id'];
$p_id = $_GET['new_p_id'];
all of these has data, so no problem here.
Here is my query:
<?php
session_start();
include_once 'order.confirmation-header.php';
include 'includes/dbh.inc.php';
$c_id = $_SESSION['u_id'];
$n_id = $_GET['n_id'];
$p_id = $_GET['new_p_id'];
$sql = "
SELECT event_id, event_name, event_date, event_time_start,
event_time_end, cusact_id, theme, reserve_date, reserve_time
FROM event_table as e
INNER JOIN package as p
ON e.package_id = p.package_id
WHERE cusact_id = $c_id AND event_id=$n_id
";
$data = mysqli_query($conn, $sql);
if(!$data){
echo("Error description: " . mysqli_error($conn));
}

Answer 1

You aren't requesting any of the package columns (by merge the table I assume you mean retrieve a record set)
SELECT event_id, event_name, event_date, event_time_start,
event_time_end, cusact_id, theme, reserve_date, reserve_time, p.*
FROM event_table as e
INNER JOIN package as p
ON e.package_id = p.package_id
WHERE cusact_id = $c_id
AND event_id=$n_id
Your code is wide open to SQL injection, and I'd really consider using the PDO API with a prepared statement.