SQL – combine rows conditionally on the value of previous row

My issue I believe is best explained by using an example:

Sample Data

SO	Customer	Product	Description	Quantity	Extension	Country
01	xxx	123	Product A	01	20.00	USA
02	yyy	456	Product B	02	25.00	China
02	yyy	456	Product B	01	12.50	China
02	yyy	789	Product C	01	50.00	Mexico
03	zzz	789	Product C	01	50.00	Mexico
03	zzz	789	Product C	01	50.00	Mexico

Desired output:

SO	Customer	Product	Description	Quantity	Extension	Country
01	xxx	123	Product A	01	20.00	USA
02	yyy	456	Product B	03	37.50	China
02	yyy	789	Product C	01	50.00	Mexico
03	zzz	789	Product C	02	100.00	Mexico

So the key issue I’m having is grouping by the SO, then if there are duplicate lines of Product, consolidating lines into one. In the real data, there could be many lines to summarize or none at all – it could all be unique.

Answer

This looks like group by:

select SO, Customer, Product, Description, sum(Quantity), sum(Extension),   Country
from t
group by SO, Customer, Product, Description, Country;

Note that quantity looks strange. Numbers in SQL are not shown with leading zeros — and numbers should be stored as numbers, not strings.