Converting associative arrays in PHP

I've been googling around and searching this forum but I haven't actually found a solution for what I need to achieve.

I'm getting an array from a db in this form

Array
(
[0] => Array
    (
        [0] => af
        [1] => Afghanistan
    )

[1] => Array
    (
        [0] => al
        [1] => Algeria
    )
)
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I need it to look like this

Array
(
    [af] => Afghanistan
    [al] => Algeria
)
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The db is sql server, this is the code I'm using to get the data

$sQueryCountries = "SELECT Country_Code,Country_Name FROM Countries WHERE Client_Id = '$client_id'";
$params = array();
$options =  array( "Scrollable" => SQLSRV_CURSOR_KEYSET );

$rResultCountries = sqlsrv_query( $db, $sQueryCountries, $params, $options );
while ( $aRow = sqlsrv_fetch_array( $rResultCountries, SQLSRV_FETCH_NUMERIC ) )
{       
    $output[] = $aRow;      
}
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