sql case then code example

Example 1: case when switch in SQL

-- Case Eg.) to retrive the MAX value of a Field 
-- if there are entries for the Field in table MAX value will be returned 
-- But if there is no entries at all for the Field in tabel MAX will return
-- Null as the output. But Using Case When we can check it out return zero 
-- or any other value if there is no enties for the Field in table..
SELECT 
CASE   -- Like Switch Case
	WHEN -- First When condition 
		(MAX(BILLID) IS NULL) -- Condition 
	THEN 1   -- output   (We can also add more When conditions like Above)
ELSE -- When WHEN Condition not Satisfied Below will be Executed. 
		(MAX(BILLID)) -- output
END 
as MAXBILLID   from  DUAL;
-- Final Output
-- If there is no entry in the Field for the table
-- BILLID
--  1
-- If there are entries MAX of that Field value from the table
-- BILLID
-- 10

Example 2: end as sql

select 
case when ID in ('1', '2', '3')
then 'Jack'
else 'Jim'
end as Person
from Table.Names

select
case when ID in ('1', '2', '3')
then 'Jack'
else 'Jim'
end Person
from Table.Names