Best way to do nested case statement logic in SQL Server

Question

I\'m writing an SQL Query, where a few of the columns returned need to be calculated depending on quite a lot of conditions.

I\'m currently using nested case stateme

Answer 1

I went through this and found all the answers super cool, however wants to add to answer given by @deejers

    SELECT
    col1,
    col2,
    col3,
    CASE
        WHEN condition1 THEN calculation1 
        WHEN condition2 THEN calculation2
        WHEN condition3 THEN calculation3
        WHEN condition4 THEN calculation4
        WHEN condition5 THEN calculation5         
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

you can make ELSE optional as its not mandatory, it is very helpful in many scenarios.

Answer 2

Wrap all those cases into one.

---

SELECT
    col1,
    col2,
    col3,
    CASE
        WHEN condition1 THEN calculation1 
        WHEN condition2 THEN calculation2
        WHEN condition3 THEN calculation3
        WHEN condition4 THEN calculation4
        WHEN condition5 THEN calculation5
        ELSE NULL         
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

Answer 3

You can combine multiple conditions to avoid the situation:

CASE WHEN condition1 = true AND condition2 = true THEN calculation1 
     WHEN condition1 = true AND condition2 = false 
     ELSE 'what so ever' END,

Answer 4

We can combine multiple conditions together to reduce the performance overhead.

Let there are three variables a b c on which we want to perform cases. We can do this as below:

CASE WHEN a = 1 AND b = 1 AND c = 1 THEN '1'
     WHEN a = 0 AND b = 0 AND c = 1 THEN '0'
ELSE '0' END,

Answer 5

You could try some sort of COALESCE trick, eg:

SELECT COALESCE(
  CASE WHEN condition1 THEN calculation1 ELSE NULL END,
  CASE WHEN condition2 THEN calculation2 ELSE NULL END,
  etc...
)

Answer 6

Here's a simple solution to the nested "Complex" case statment: --Nested Case Complex Expression

select  datediff(dd,Invdate,'2009/01/31')+1 as DaysOld, 
    case when datediff(dd,Invdate,'2009/01/31')+1 >150 then 6 else
        case when datediff(dd,Invdate,'2009/01/31')+1 >120 then 5 else 
            case when datediff(dd,Invdate,'2009/01/31')+1 >90 then 4 else 
                case when datediff(dd,Invdate,'2009/01/31')+1 >60 then 3 else 
                    case when datediff(dd,Invdate,'2009/01/31')+1 >30 then 2 else 
                        case when datediff(dd,Invdate,'2009/01/31')+1 >30 then 1 end 
                    end
                end
            end
        end
    end as Bucket
from rm20090131atb

Just make sure you have an end statement for every case statement