How to combine rows dynamically - sql-server

Question

I have a table with many columns (even number of columns). Now I need to combine the second column and third column, the forth and fifth column, sixth and seventh column....etc. How to achieve this?
I tried static one, but what about dynamic one. Assume that there are 100 or more columns.
create table tb11 ( [id] int,[A] varchar(20),[B] varchar(20),
[C] varchar(20),[D] varchar(20))
insert into tb11 values
(1,'a','b','c','d'),
(2,'e','f','g','h'),
(3,'i','j','k','l')
select * from tb11
/*
id A B C D
---- --- ---- --- ----
1 a b c d
2 e f g h
3 i j k l
*/
select id,
[A] + [B] as '1' ,
[C] + [D] as '2'
from tb11
/*output with 3 columns
id 1 2
---- ----- ------
1 ab cd
2 ef gh
3 ij kl
*/

Answer 1

Try this
DECLARE #SQL NVARCHAR(MAX)
SELECT #SQL = (
SELECT '
' +
STUFF((
SELECT ', ' + c.name + ' + ' + c2.name + ' AS [' + c.name + c2.name +']'
FROM sys.columns c
INNER JOIN sys.columns c2 ON c2.object_id = c.object_id
AND c2.column_id = c.column_id + 1
WHERE c.[object_id] = o.[object_id]
AND c.column_id > 1
AND c.column_id % 2 = 0
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'), 1, 2, 'SELECT id, ') + '
FROM [' + SCHEMA_NAME(o.[schema_id]) + '].[' + o.name + ']' -- select *
FROM sys.objects o
WHERE o.[type] = 'U'
AND o.is_ms_shipped = 0
AND [name] = 'tb11'
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)')
PRINT #SQL
EXEC sys.sp_executesql #SQL

Answer 2

You may use schema of tables to get the list of columns and create dynamic columns name from them.
Similarly by using that schema only create you table script for new structure.
Try this:
GO
;with cte as (
select ORDINAL_POSITION as slno, COLUMN_NAME from information_schema.columns where table_name = 'tb11'
)
select * into #tab_col from cte
declare #max int
set #max = (select Count(*) -1 from #tab_col)
declare #loop int
set #loop = 0
create table newtab (
id int )
declare #columns nvarchar(max) = ''
declare #values nvarchar(max) = ''
while(#Loop <= (#Max/2))
Begin
declare #Col1 varchar(100)
declare #Col2 varchar(100)
set #Col1 = (select Column_name from #tab_col where slno = #Loop+2)
set #Col2 = (select Column_name from #tab_col where slno = #Loop+3)
declare #alter nvarchar(max)
set #alter = ' Alter table newtab add [' + cast(((#Loop/2)+1) as varchar(100)) + '] nvarchar(max) '
set #columns = #columns + ',[' + (select cast(((#Loop/2)+1) as varchar(100))) + ']'
set #values = #values + ',''' + #Col1 + #Col2 + ''''
exec sp_executesql #alter
set #loop = #loop + 2
End
set #values =( select substring( #values, 2, len(#values)))
select #values
set #columns =( select substring( #columns, 2, len(#columns)))
select #columns
declare #altertab nvarchar(max)
set #altertab = ' insert into newtab ( id, ' + #columns + ' ) values ( 1, ' + #values + ' )'
exec sp_executesql #altertab
drop table newtab
Drop table #tab_col
GO
This will not exactly give you your answer but you'll get some idea.