SQL - How to transpose several columns?

Question

I have a table in an IBM DB2 database; let's call it table_1. It looks a bit like this:

customer	info	offer_type_a_sales	offer_type_b_sales	offer_type_c_sales
AA	X	10	20	30
BB	Y	0	10	15
CC	X	20	0	30

What I'd like to do is transpose the offer type columns to create a single column flagging offer type and a single column showing sales. Does anyone know how best to do this please?

The desired output should look like this:

customer	info	offer_type	sales
AA	X	a	10
AA	X	b	20
AA	X	c	30
BB	Y	b	10
BB	Y	c	15
CC	X	a	20
CC	X	c	30

Answer 1

There might be a way to unpivot but here's an alternative solution using union.

select customer, info, 'a' as offer_type, offer_type_a_sales as sales from table_1
union
select customer, info, 'b', offer_type_b_sales from table_1
union 
select customer, info, 'c', offer_type_c_sales from table_1

customer	info	offer_type	sales
AA	X	a	10
AA	X	b	20
AA	X	c	30
BB	Y	a	0
BB	Y	b	10
BB	Y	c	15
CC	X	a	20
CC	X	b	0
CC	X	c	30

If you don't want the zero rows then add a where clause.