I've got this table:

```
id    |   payment_id   | quantity  |  unit cost
1           633             1            750  
2           633             1            750 
3           632             2            750 
4           632             2            750 

```

What I need is :

```
payemnt_id  |   total
    633           1500
    632           3000 

```

You can also think of this as Countries and then you are trying to find the total for each Country. I was sure there were some tutorials like this but could not find by STFW.