How to compare two columns in the CASE statement - sql

Question

I have two columns Speed_A and Speed_B.
Now I will compare both columns and will select the higher one in a new table.
Something like this:
SELECT ...
CASE
WHEN a.Speed_A > a.Speed_B THEN a.Speed_A
WHEN a.Speed_A < a.Speed_B THEN a.Speed_B
ELSE 0 --unknown
END as SpeedLimit,
How does it work?

Answer 1

Assuming your speeds are numerically typed you might get this as easy as:
SELECT CASE WHEN a.Speed_A>a.Speed_B THEN a.Speed_A ELSE a.Speed_B END AS SpeedLimit
[...FROM SomeWhere...]
Your ELSE will only occur, when A and B are equal, In this case it doesn't matter, which one you return.
UPDATE
column´s data type is integer. And yes there are nulls
If A is null return B, If b is null return A (works for A and B is null implicitly). Otherwise both are not null and therefore the statement above should be perfect
SELECT CASE WHEN a.Speed_A IS NULL THEN a.Speed_B
ELSE CASE WHEN a.Speed_B IS NULL THEN a.Speed_A
ELSE CASE WHEN a.Speed_A>a.Speed_B THEN a.Speed_A ELSE a.Speed_B
END
END
END AS SpeedLimit
FROM Dummy
[...FROM SomeWhere...]

Answer 2

You can create a inline max function that return the max between two values something like:
create function dbo.InlineMax(#val1 int, #val2 int)
returns int
as
begin
if #val1 > #val2
return #val1
return isnull(#val2,#val1)
end
and you can use it like this:
SELECT dbo.InlineMax(a.Speed_A, a.Speed_B)
FROM ....

Answer 3

Nested Case and Case without Column Name
select
CASE ColumnName
WHEN 'enter value on which you want to execute Than Block'
THEN
CASE ColumnName
WHEN 1 THEN 'return value or Column Name'
ELSE 'return value or Column Name in case of else'
END
WHEN 'another condition, value of column on which you want to execute then block'
THEN
CASE WHEN 'Condition etc => ColumnName > 5 or ColumnName ='abc' ' THEN 'return value or column name' ELSE 'return value or column name' END
ELSE 'return value or column name'
END as status
FROM TableName