What's The More Eficient Method?

Hello, I've a table "TblSales" with this structure: Year (integer), CustomerId (integer) and Sales (float).

SELECT Year, CustomerId, Sales FROM TblSales

Year;CustomerId;Sales
2000;1;100
2000;1;50
2000;2;200
2001;1;10
2001;2;20
etc...

I've 10 distinct CustomerId (from 1 to 10)

I want to make a row for every year with x columns (1 for every diferent CustomerId) with the sum of sales of this Customer on this year.

I've thounsdands rows. What's the more eficient method?

Thanks