根据SQL查询的前一个CASE语句制作CASE语句

Question

I currently am working with SQL Server 2012 and trying to figure out how to get results from a CASE statement.

So currently I have a CASE statement to calculate an AgeBusiness field that I currently am using to find the Business Age of requests. This is the code I have for it:

CASE    WHEN A.[End_Date] > A.[Start_Date] THEN C2.[BUS_DY_OF_CAL_NUM] - C1.[BUS_DY_OF_CAL_NUM] 
        WHEN A.[End_Date] IS NULL and A.[Start_Date] IS NOT NULL THEN C3.[BUS_DY_OF_CAL_NUM] - C1.[BUS_DY_OF_CAL_NUM]
        WHEN A.[End_Date] = A.[Start_Date] THEN 1
END AS AgeBusiness

Basically, if End Date is greater than Start Date, use End Date - Start Date to calculate. If no End Date, use GETDATE() - Start Date to calculate. If they're equal, then 1 business day.

Anyways, I have this AgeBusiness field and am trying to either use this field or data from this field to calculate a new Case When statement to calculate requirements.

In a perfect world my CASE statement would go something like this:

CASE WHEN AgeBusiness >= 0 AND AgeBusiness <11 AND Name = "RequirementA" Then 1 
     WHEN AgeBusiness >= 0 AND AgeBusiness <8 AND Name = "RequirementB" Then 1  
     WHEN AgeBusiness >= 0 AND AgeBusiness <181 AND Name = "RequirementC" Then 1
     WHEN AgeBusiness >= 0 AND AgeBusiness <8 AND Name = "RequirementD" Then 1
     WHEN AgeBusiness >= 0 AND AgeBusiness <11 AND Name = "RequirementE" Then 1
     WHEN AgeBusiness >= 0 AND AgeBusiness <16 AND Name = "RequirementF" Then 1
End AS WithinRequirements

Basically I want to make a new case statement called Within Requirements where if it fell within a certain amount of days and had a particular name, then it would be yes or in this case 1. The name field already exists from a table that I can pull in. Though one of the requirements for making WithinRequirements requires the AgeBusiness to exist, which the fields would be created in query at same time...so that's not possible.

Is there a way to use the info from AgeBusiness that I put above to create WithinRequirements somehow? The goal is to figure this out in a query...even if it means a long winded query.

Answer 1

Use CROSS APPLY for intermediate variables

SELECT 
CASE WHEN AgeBusiness >= 0 AND AgeBusiness <11 AND Name = "RequirementA" Then 1 
     WHEN AgeBusiness >= 0 AND AgeBusiness <8 AND Name = "RequirementB" Then 1  
     WHEN AgeBusiness >= 0 AND AgeBusiness <181 AND Name = "RequirementC" Then 1
     WHEN AgeBusiness >= 0 AND AgeBusiness <8 AND Name = "RequirementD" Then 1
     WHEN AgeBusiness >= 0 AND AgeBusiness <11 AND Name = "RequirementE" Then 1
     WHEN AgeBusiness >= 0 AND AgeBusiness <16 AND Name = "RequirementF" Then 1
End AS WithinRequirements
FROM  A 
CROSS APPLY (
   SELECT CASE WHEN A.[End_Date] > A.[Start_Date] THEN C2.[BUS_DY_OF_CAL_NUM] - C1.[BUS_DY_OF_CAL_NUM] 
           WHEN A.[End_Date] IS NULL and A.[Start_Date] IS NOT NULL THEN C3.[BUS_DY_OF_CAL_NUM] - C1.[BUS_DY_OF_CAL_NUM]
           WHEN A.[End_Date] = A.[Start_Date] THEN 1
        END AS AgeBusiness
) vars

Answer 2

If when A.[End_Date] is null will C2.[BUS_DY_OF_CAL_NUM] also be null you can rewrite the first case statement like this:

 ABS(COALESCE(COALESCE(C2.[BUS_DY_OF_CAL_NUM],C3.[BUS_DY_OF_CAL_NUM])-C1.[BUS_DY_OF_CAL_NUM],1))

You also use BETWEEN in a case statement and operate on a single value so rewrite the 2nd one like this:

CASE ABS(COALESCE(COALESCE(C2.[BUS_DY_OF_CAL_NUM],C3.[BUS_DY_OF_CAL_NUM])-C1.[BUS_DY_OF_CAL_NUM],1))
     WHEN AgeBusiness >= 0 AND AgeBusiness <11 AND Name = "RequirementA" Then 1 
     WHEN BETWEEN 0 AND 11  AND Name = "RequirementB" Then 1  
     WHEN BETWEEN 0 AND 181 AND Name = "RequirementC" Then 1
     WHEN BETWEEN 0 AND 8   AND Name = "RequirementD" Then 1
     WHEN BETWEEN 0 AND 11  AND Name = "RequirementE" Then 1
     WHEN BETWEEN 0 AND 16  AND Name = "RequirementF" Then 1
End AS WithinRequirements

I believe this query is less "long winded" than your original.