Variable as Column Name SQL Server - sql-server

Question

I want to know, if exist a way to create a CURSOR with a variable column names
Example:
I have this table:
Translation image for text
ID | TEST1 | TEST2 | TEST3
7 1 3 1
8 2 3 4
9 3 4 5
10 3 3 1
11 2 3 4
12 3 4 5
13 1 3 1
14 2 3 4
15 3 4 5
SQL Code:
DECLARE
#count int,
#columnX varchar(5),
#aux2previous int,
#aux2 int,
#aux1 int,
#columnXResult int,
#id int;
SET #aux2previous = 0;
SET #count = 1;
SET #columnX = 'test' + count;
DECLARE cursor1 CURSOR FOR
SELECT ID, #columnX FROM table
OPEN cursor1
FETCH NEXT FROM cursor1 INTO #id,#columnXResult
...
SET #aux1 = #columnXResult+ #aux2previous
SET #aux2 = #aux2previous + 1
SET #string = 'SXW_'+#columnX+'_'+#aux1+'<>'+#aux2
INSERT INTO tblAuxiliary VALUES(#aux1,#aux2,#string)
SET #count = #count + 1;
SET #aux2previous = #aux2
...
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Foreach row in my first table i have a new row here:
for column Test1
AUX1 | AUX2 | STRING
1 1 SXW_Test1_1<>1
3 2 SXW_Test1_3<>2
for column Test2
AUX1 | AUX2 | STRING
3 1 SXW_Test2_3<>1
6 4 SXW_Test2_6<>4
for column Test3
AUX1 | AUX2 | STRING
1 1 SXW_Test3_1<>1
5 2 SXW_Test3_5<>2
when i do with #columnX
SELECT ID, #columnX FROM table
i got this error:
Conversion failed when converting the varchar value 'test1' to data type int
I see something like #sql = 'select '+#columnX ..., but i need to exec it and i can't do this with cursor.

Answer 1

It is example how use dynamic sql and cursor:
create table test (
t1 int not null,
t2 varchar(10) not null
)
declare #query varchar(1000)
select #query = '
declare #column int
declare query cursor for
select t'+cast(1 as varchar(1))+' from test
open query
fetch next from query into #column
while(##FETCH_STATUS=0)
begin
select #column
fetch next from query into #column
end
close query
deallocate query
'
exec (#query)

Answer 2

There's no way to create a cursor with variable column names unless you use dynamic SQL: you build up a string of SQL code and use EXEC sp_executesql to run it. It's messy and difficult to get right, but you can do it with some trial and error (preferably on a development system, not in production).
FWIW, I think some of the comments above a being a little harsh because they've forgotten what it's like to start out in their field: you're doing fine. Cursors are often misused by web developers who think procedurally instead of "set based", but I still use them occasionally where they make sense (or are just easier). If you want, you can post a new question with more details about what you're trying to accomplish and ask "how can I get rid of this cursor". But if the performance with the cursor is okay, don't worry about it.
HTH!

Answer 3

Check this out.
DECLARE #table TABLE(ID INT,test1 INT,test2 INT,test3 INT)
INSERT INTO #TABLE VALUES
(7,1,3,1),(8,2,3,4),(9,3,4,5),(10,3,3,1),
(11,2,3,4),(12,3,4,5),(13,1,3,1),(14,2,3,4),
(15,3,4,5)
SELECT top 2
t.test1 AUX1,(t.test1+T.prev_test1) AUX2,concat('SXW_Test1_',t.test1,'<>',(t.test1+T.prev_test1)) as string FROM
(
SELECT test1,
LAG(test1,1,0) OVER (ORDER BY ID) prev_test1
FROM #table
) t
union all
SELECT top 2
t.test2 AUX1,(t.test2+T.prev_test2) AUX2,concat('SXW_Test2_',t.test2,'<>',(t.test2+T.prev_test2)) as string FROM
(
SELECT test2,
LAG(test2,1,0) OVER (ORDER BY ID) prev_test2
FROM #table
) t
union all
SELECT top 2
t.test3 AUX1,(t.test3+T.prev_test3) AUX2,concat('SXW_test3_',t.test3,'<>',(t.test3+T.prev_test3)) as string FROM
(
SELECT test3,
LAG(test3,1,0) OVER (ORDER BY ID) prev_test3
FROM #table
) t