Query returns two lines - sql-server

Question

I have a table that has a column called type which has either a value of invoiced or order and then another column holding the value along with a column holding the customer number etc.
I have written a script :-
select
customer,
(CASE WHEN TYPE = 'INVOICED' THEN SUM(INVTOTAL) else 0 END) AS INVTOTAL,
(CASE WHEN TYPE = 'ORDERS' THEN SUM(INVTOTAL) else 0 END) AS ORDERTOTAL
from
salestable
Why does it return the following?
customer INVTOTAL ORDERTOTAL
Joe Bloggs 1000 0
Joe Bloggs 0 1300
instead of
customer INVTOTAL ORDERTOTAL
Joe Bloggs 1000 1300
Sorry to ask such a novice question but I am new to SQL and learning it...
Thanks for any help!

Answer 1

Your query was missing a group by. Also use sum around case to avoid multiple rows.
select customer,
sum(CASE WHEN TYPE = 'INVOICED' THEN INVTOTAL else 0 END) AS INVTOTAL,
sum(CASE WHEN TYPE = 'ORDERS' THEN INVTOTAL else 0 END) AS ORDERTOTAL
from salestable
group by customer

Answer 2

You need to do a group by with the customer that will avoid the multiple rows.check the fiddle below.
create table tb1
(customer varchar(25),
type varchar(25),
invoice numeric(18,2)
);
insert into tb1(customer,type,invoice) values('Joe Bloggs','INVOICED',1000);
insert into tb1(customer,type,invoice) values('Joe Bloggs','ORDERS',1000);
select customer,
sum(CASE WHEN TYPE = 'INVOICED' THEN sum(invoice) else 0 END) AS INVTOTAL,
sum(CASE WHEN TYPE = 'ORDERS' THEN sum(invoice) else 0 END) AS ORDERTOTAL
from tb1
group by customer
fiddle with example
You need to put the entire case statment inside sum()
inorder to avoid grouping by type also else you will get this below error
Column 'tb1.type' is invalid in the select list because it is
not contained in either an aggregate function or the GROUP BY clause.

Answer 3

Because select returns a row for each row in the table matching the where filters. If no filters, then a result row for every row in table. If you want to "join" the rows, you could try grouping by the customer, like:
SELECT customer,
SUM(CASE WHEN TYPE = 'INVOICED' THEN INVTOTAL ELSE 0 END) as INVTOTAL,
SUM(CASE WHEN TYPE = 'ORDERS' THEN INVTOTAL ELSE 0 END) as ORDERTOTAL
FROM salestable
GROUP BY customer