CODEWITHSUNDEEP
sqlsql-serversql-server-2005selectnested
Sophia
Sophia

Reputation: 5823

Best way to do nested case statement logic in SQL Server

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 statements, but its getting messy. Is there a better (more organised and/or readable) way?

(I am using Microsoft SQL Server, 2005)

A simplified example:

SELECT
    col1,
    col2,
    col3,
    CASE
        WHEN condition 
        THEN
            CASE
                WHEN condition1 
                THEN
                    CASE 
                        WHEN condition2
                        THEN calculation1
                        ELSE calculation2
                    END
                ELSE
                    CASE 
                        WHEN condition2
                        THEN calculation3
                        ELSE calculation4
                    END
            END
        ELSE 
            CASE 
                WHEN condition1 
                THEN 
                    CASE
                        WHEN condition2 
                        THEN calculation5
                        ELSE calculation6
                    END
                ELSE
                    CASE
                        WHEN condition2 
                        THEN calculation7
                        ELSE calculation8
                    END
            END            
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

Upvotes: 242

Views: 1065392

Answers (10)

esenkaya
esenkaya

Reputation: 408

Less complex format. Make sure keep the indentation as it is to not to be lost in ENDs.

SELECT 
CASE WHEN 1=1 THEN 
            CASE 
                WHEN 11=11 THEN CASE WHEN 111=111 THEN '1-11-111' END
                WHEN 12=12 THEN CASE WHEN 122=122 THEN '1-12-122' END
                WHEN 13=13 THEN CASE WHEN 133=133 THEN '1-13-133' END 
            END
        ELSE
            CASE WHEN 2=2 THEN 
                CASE 
                    WHEN 21=21 THEN CASE WHEN 211=211 THEN '2-21-211' END
                    WHEN 22=22 THEN CASE WHEN 222=222 THEN '2-22-222' END
                END
            ELSE
                CASE WHEN 3=3 THEN 
                    CASE 
                        WHEN 31=31 THEN CASE WHEN 311=311 THEN '3-31-311' END
                        WHEN 32=32 THEN CASE WHEN 322=322 THEN '3-32-322' END
                    END
                ELSE
                    CASE WHEN 4=4 THEN 
                        CASE 
                            WHEN 41=41 THEN CASE WHEN 411=411 THEN '4-41-411' END
                            WHEN 42=42 THEN CASE WHEN 412=412 THEN '4-42-412' END
                        END
                    ELSE
                        CASE 
                            WHEN 51=51 THEN CASE WHEN 511=511 THEN '51-511' END
                            WHEN 52=52 THEN CASE WHEN 512=512 THEN '52-512' END
                            WHEN 53=53 THEN CASE WHEN 513=513 THEN '53-513' END
                            WHEN 54=54 THEN CASE WHEN 514=514 THEN '54-514' END
                        END
                    END
                END
            END
        END
        AS Sku
FROM YourTable

Upvotes: 2

ssingh
ssingh

Reputation: 643

You can combine multiple conditions to avoid the situation:

CASE WHEN condition1 = true AND condition2 = true THEN calculation1 
     WHEN condition1 = true AND condition2 = false THEN calculation2
     ELSE 'what so ever' END,

Upvotes: 55

Sandy
Sandy

Reputation: 279

This example might help you, the picture shows how SQL case statement will look like when there are if and more than one inner if loops

enter image description here

Upvotes: 4

user3065757
user3065757

Reputation: 503

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.

Upvotes: 4

Jims2885
Jims2885

Reputation:

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

Upvotes: 16

Sanjeev Singh
Sanjeev Singh

Reputation: 4066

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,

Upvotes: 8

Deejers
Deejers

Reputation: 3507

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

Upvotes: 124

beach
beach

Reputation: 8640

I personally do it this way, keeping the embedded CASE expressions confined. I'd also put comments in to explain what is going on. If it is too complex, break it out into function.

SELECT
    col1,
    col2,
    col3,
    CASE WHEN condition THEN
      CASE WHEN condition1 THEN
        CASE WHEN condition2 THEN calculation1
        ELSE calculation2 END
      ELSE
        CASE WHEN condition2 THEN calculation3
        ELSE calculation4 END
      END
    ELSE CASE WHEN condition1 THEN 
      CASE WHEN condition2 THEN calculation5
      ELSE calculation6 END
    ELSE CASE WHEN condition2 THEN calculation7
         ELSE calculation8 END
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

Upvotes: 43

Chris KL
Chris KL

Reputation: 5002

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...
)

Upvotes: 223

Steven A. Lowe
Steven A. Lowe

Reputation: 61233

a user-defined function may server better, at least to hide the logic - esp. if you need to do this in more than one query

Upvotes: 8

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