What is a better alternative to procedural approach to produce a string based on columns? - sql

Question

I am working on making string based on column values. Example:
SELECT #Registered = a.hasRegistered
,#Subscribed = a.hasSubscribed
FROM AuthorData a
WHERE a.authorId = 10 --#AUTHORID
IF (#Registered = 1)
SET #ReturnString = #ReturnString + '0,'
IF (#Subscribed = 1)
SET #ReturnString = #ReturnString + '1,'
IF EXISTS (
SELECT TOP 1 name
FROM AUTHORDATA AS A
INNER JOIN AUHTORPROFILE B on A.AUTHORID=B.AUTHORID
INNER JOIN AUTHORHISTORY C ON B.AUTHORPROFILEID=C.AUTHORPROFILEID
WHERE ISNULL(AUTHORDATA.authorId, 0) = 10 --#AUTHORID
)
BEGIN
SET #ReturnString = #ReturnString + '10,'
END
select CONVERT(NVARCHAR(50), STUFF(#ReturnString, LEN(#ReturnString), 1, ''))
This performs the calculation for 1 author (based on WHERE clause IN 2 places -> authorId=10)
I can make this into a function and then call from a select query as follows:
SELECT *,FN_CALCUALTE_OPTIONS(AUTHORID)
FROM AUTHORDATA
I want to ask if there is any way so I can do the calculations in the above SELECT query rather than create the function?
I have tried:
SELECT *,CASE WHEN A.hasRegistered=1 THEN '0,' ELSE '' END +
CASE WHEN A.hasSubscribed=1 THEN '1,' ELSE '' END
FROM AUTHORDATA as A
How can I have the exists part of select?

Answer 1

Pretty sure you can put them all together into a single query as follows. If you didn't need the final stuff you would just have a regular query, but because you need to use the results twice in the stuff CROSS APPLY is a convenient way to calculate it once and use it twice. Also you can correlate your sub-query since you are using the same AuthorData record.
SELECT CONVERT(NVARCHAR(50), STUFF(X.ReturnString, LEN(X.ReturnString), 1, ''))
FROM AuthorData a
CROSS APPLY (
VALUES
(
CASE WHEN a.hasRegistered = 1 THEN '0,' ELSE '' END
+ CASE WHEN a.hasSubscribed = 1 THEN '1,' ELSE '' END
+ CASE WHEN EXISTS (
SELECT 1
FROM AUHTORPROFILE B
INNER JOIN AUTHORHISTORY C ON B.AUTHORPROFILEID = C.AUTHORPROFILEID
WHERE B.AUTHORID = a.AuthorId
)
THEN '10,' else '' end
)
) AS X (ReturnString)
WHERE a.AuthorId = 10 --#AUTHORID

Answer 2

The easiest way IMO is to move your criteria being found via EXISTS to an OUTER APPLY. Like so:
SELECT
CONVERT(NVARCHAR(50), STUFF(calc.ReturnString, LEN(calc.ReturnString), 1, ''))
FROM
AUTHORDATA AS A
OUTER APPLY (SELECT TOP (1)
1 AS Found
FROM
AUHTORPROFILE AS B
INNER JOIN AUTHORHISTORY AS C ON B.AUTHORPROFILEID = C.AUTHORPROFILEID
WHERE
B.authorId = A.authorId) AS lookup_author
/*outer apply here just for readibility in final select*/
OUTER APPLY (SELECT
CONCAT(CASE WHEN A.hasRegistered = 1 THEN '0,' ELSE '' END
,CASE WHEN A.hasRegistered = 1 THEN '1,' ELSE '' END
,CASE WHEN lookup_author.Found = 1 THEN '10,' ELSE '' END) AS ReturnString) AS calc;
Then you can use lookup_author.Found = 1 to determine that it was found in your lookup. From there, you just have to apply the rest of your conditions correctly via CASE statements and then use your final SELECT over the result.

Answer 3

You can put a single CASE statement and get data as given below. Make sure that you are covering every possible condition.
SELECT *, CASE WHEN a.Registered =1 AND a.Subscribed =1
AND EXISTS (SELECT TOP 1 1
FROM AUHTORPROFILE B on
INNER JOIN AUTHORHISTORY C ON B.AUTHORPROFILEID=C.AUTHORPROFILEID
WHERE B.AUTHORID =A.AUTHORID) THEN '0,1,10'
WHEN a.Registered =1 AND a.Subscribed =0
AND EXISTS (SELECT TOP 1 1
FROM AUHTORPROFILE B on
INNER JOIN AUTHORHISTORY C ON B.AUTHORPROFILEID=C.AUTHORPROFILEID
WHERE B.AUTHORID =A.AUTHORID) THEN '0,10'
WHEN a.Registered =0 AND a.Subscribed =1
AND EXISTS (SELECT TOP 1 1
FROM AUHTORPROFILE B on
INNER JOIN AUTHORHISTORY C ON B.AUTHORPROFILEID=C.AUTHORPROFILEID
WHERE B.AUTHORID =A.AUTHORID) THEN '1,10'
WHEN a.Registered =0 AND a.Subscribed =0
AND EXISTS (SELECT TOP 1 1
FROM AUHTORPROFILE B on
INNER JOIN AUTHORHISTORY C ON B.AUTHORPROFILEID=C.AUTHORPROFILEID
WHERE B.AUTHORID =A.AUTHORID) THEN '10'
END AS CalculateOptions
FROM AUTHORDATA AS a