do i need to rewrite the case statement for every field? - sql

Question

The case condition for two columns is same.in the below statement am using this twice but for different column, is there any other way for not repeating the condition twice ??
case [CPHIL_AWD_CD]
when ' ' then 'Not Applicable/ Not a Doctoral Student'
when 'X' then 'Not Applicable/ Not a Doctoral Student'
when 'N' then 'NO'
when 'Y' then 'YES'
end as CPHIL_AWD_CD
,case [FINL_ORAL_REQ_CD]
when ' ' then 'Not Applicable/ Not a Doctoral Student'
when 'X' then 'Not Applicable/ Not a Doctoral Student'
when 'N' then 'NO'
when 'Y' then 'YES'
end as FINL_ORAL_REQ_CD

Answer 1

Just create a table (temp?) with the mapping
CREATE TABLE [Constants]
(
[ID] nvarchar(1) PRIMARY KEY,
[Text] nvarchar(max)
)
INSERT INTO [Constants] VALUES (' ', 'Not Applicable/ Not a Doctoral Student')
INSERT INTO [Constants] VALUES ('X', 'Not Applicable/ Not a Doctoral Student')
INSERT INTO [Constants] VALUES ('N', 'No')
INSERT INTO [Constants] VALUES ('Y', 'Yes')
and perform an inner join
SELECT C1.Text AS CPHIL_AWD_CD, C2.Text AS FINL_ORAL_REQ_CD, ...
FROM YourTable T
INNER JOIN Constants C1 ON C1.ID = T.CPHIL_AWD_CD
INNER JOIN Constants C2 ON C2.ID = T.FINL_ORAL_REQ_CD

Answer 2

A variation on thepirat000's answer:
-- Sample data.
declare #Samples as Table (
Frisbee Int Identity Primary Key, Code1 Char(1), Code2 Char(2) );
insert into #Samples values ( 'Y', 'N' ), ( ' ', 'Y' ), ( 'N', 'X' );
select * from #Samples;
-- Handle the lookup.
with Lookup as (
select * from ( values
( ' ', 'Not Applicable/ Not a Doctoral Student' ),
( 'X', 'Not Applicable/ Not a Doctoral Student' ),
( 'N', 'No' ),
( 'Y', 'Yes' ) ) as TableName( Code, Description ) )
select S.Code1, L1.Description, S.Code2, L2.Description
from #Samples as S inner join
Lookup as L1 on L1.Code = S.Code1 inner join
Lookup as L2 on L2.Code = S.Code2;
The lookup table is created within a CTE and referenced as needed for multiple columns.
Update: The table variable is now blessed with a primary key for some inexplicable reason. If someone can actually explain how it will benefit performance, I'd love to hear it. It isn't obvious from the execution plan.

Answer 3

As per the suggestion from Dijkgraaf, here is the solution:
Create a function with the logic in it and call that in the select statement:
CREATE FUNCTION dbo.GetCaseValue (#val varchar(50))
RETURNS varchar(50)
WITH EXECUTE AS CALLER
AS
BEGIN
return (select case #val
when ' ' then 'Not Applicable/ Not a Doctoral Student'
when 'X' then 'Not Applicable/ Not a Doctoral Student'
when 'N' then 'NO'
when 'Y' then 'YES'
end)
END
And call it like:
select dbo.GetCaseValue([CPHIL_AWD_CD]) as 'CPHIL_AWD_CD',
dbo.GetCaseValue([FINL_ORAL_REQ_CD]) as 'FINL_ORAL_REQ_CD'

Answer 4

Not really. What you are doing is, to the best of my knowledge, correct.
You COULD make a user defined function as below, but the benefits are .. subjective.
CREATE FUNCTION dbo.ufnMungeIt (
#In NVARCHAR(1)
)
RETURNS NVARCHAR(255)
BEGIN
RETURN CASE #In
when ' ' then 'Not Applicable/ Not a Doctoral Student'
when 'X' then 'Not Applicable/ Not a Doctoral Student'
when 'N' then 'NO'
when 'Y' then 'YES'
END
END
--
SELECT dbo.ufnMungeIt([CPHIL_AWD_CD]) AS CPHIL_AWD_CD,
dbo.ufnMungeIt([FINL_ORAL_REQ_CD]) AS FINL_ORAL_REQ_CD