尝试使用函数my $ connection变量访问位于不同目录中的数据库

As the title says, I have a database connection file in a different directory and im trying to access that inside a function, it works if its not inside a function as I have been using through out my web development, but now that I need to access inside a function it does not work.

 function getSubCat($mainCat){
    include"../sql/sqln.php";
    $sql = "SELECT SUB_CAT FROM CATEGORIES WHERE CAT = '$mainCat' GROUP BY SUB_CAT";
    $getQuery = $connection->query($sql);
}

PHP storms points out this error. unidentified variable 'connection'

Database connection

    <?php
       session_start();
       $username = "xxx";
       $password = "xxxx";
       $database = "xxx";
       $localhost = "xxxx";
       $connection = mysqli_connect($localhost, $username, $password, $database);
?>

UPDATE:

I tested it and the function is actually working, but PHP storms still give me an warning/error (unidentified variable 'connection'). not sure if I should just ignore it since its actually working.

Send the $connection variable as a parameter:

function getSubCat($mainCat,$connection){
    include"../sql/sqln.php";
    $sql = "SELECT SUB_CAT FROM CATEGORIES WHERE CAT = '$mainCat' GROUP BY SUB_CAT";
    $getQuery = $connection->query($sql);
}

and when you call the function do it this way:

getSubCat($mainCat,$connection)