I'm trying to get the results of my best selling products using SQL.

My table is `order_items` which has the following columns.

```
id|product_id|qty

```

As there is a `QTY` field I have to somehow count or group each by product ID then sum the qty, then only return the top 5 selling items.

So the data looks kind of like below.

```
id|product_id|qty
-------------------------
 1|   1      |   1
 2|   1      |   3 
 3|   2      |   3 
 4|   2      |   1 
 5|   1      |   7

```

... and so on 

Not to sure about how to go about this, any help is much appreciated.

Database system used is MySQL