Compare values of two columns then select the larger value

Question

I need to query a table and select 3 of the values of 4 columns. I need to compare the values of the 3rd column and the fourth column and select the larger value.

For ex

Answer 1

Just so we don't return null:

SELECT  IIF( a > b, a, COALESCE( a, b )) -- coalesce or isnull
FROM wherever

Here's a query to test it:

with whatever as (
  select null as a, 1 as b
  UNION
  select 1 as a, null as b
  union
  select 1 as a, 0 as b
  union
  select 0 as a, 1 as b
  union
  select null as a, null as b
)
select( iif( a > b, a, isnull( b, a )))
from whatever

Should return

null
1
1
1
1