How to sum all the customers in DS01,02,03 into DS?

select sum(case when Ticket='DS01' OR 'DSO2' OR 'DS03' THEN customer ELSE 0 END) AS DS sum(case when Ticket='MSO2' OR 'MS03' THEN customer ELSE 0 END) AS MS from table group by ticket unsure how to bring in addition condition within "THEN and ELSE " part
