Using sub-query to generate case statements - sql-server

Question

What i am trying to accomplish is comparing two rows to each other pointing out the differences from row to row. Each row has quite a few columns and I was trying to make it easily visible for which ones had changed. Code below is my thoughts, but I know this won't work, but is a start.
SELECT
(SELECT concat('Case WHEN T1.', column_name, ' <> T2.', column_name, ' THEN ''', column_name, ' Changed Values('' + CONVERT(varchar(100), T1.', column_name, ') + '', '' + CONVERT(varchar(100), T2.', column_name, ') + '')'' ELSE '''' END AS ', column_name)
FROM information_schema.columns
WHERE table_name = 'Table')
FROM
(
SELECT * FROM Table
WHERE ID = '13'
) AS T1
JOIN
(
SELECT * FROM Table
WHERE ID = '2006'
) AS T2
ON T1.CreateTimeStamp = T2.CreateTimeStamp
I got the idea because below this works fine, but I would like this to be potentially reusable code for other table without having to type out tens or hundreds of columns each time.
SELECT
Case WHEN T1.R1<> T2.R1 THEN 'Changed Values(' + CONVERT(varchar(100),T1.R1) + ', ' + CONVERT(varchar(100),T2.R1) + ')' ELSE '' END AS R1,
Case WHEN T1.R2<> T2.R2 THEN 'Changed Values(' + CONVERT(varchar(100),T1.R2) + ', ' + CONVERT(varchar(100),T2.R2) + ')' ELSE '' END AS R2
FROM
(
SELECT * FROM Table
WHERE ID = '13'
) AS T1
JOIN
(
SELECT * FROM Table
WHERE ID = '2006'
) AS T2
ON T1.CreateTimeStamp = T2.CreateTimeStamp
For the this example please assume CreateTimeStamp always equals each other between the two rows.

Answer 1

You would need to create the whole query as dynamic SQL. Note that I'm using QUOTENAME() to prevent SQL Injection from weirdly named columns. I'm also trying to keep a format for the code, so I won't get headaches when debugging.
DECLARE #SQL NVARCHAR(MAX);
SELECT #SQL = N' SELECT ' + NCHAR(10)
--Concatenate all columns except ID and CreateTimeStamp
+ STUFF(( SELECT REPLACE( CHAR(9) + ',CASE WHEN T1.<<ColumnName>> <> T2.<<ColumnName>> ' + CHAR(10)
+ CHAR(9) + CHAR(9) + 'THEN ''Changed Values('' + CONVERT(varchar(100),T1.<<ColumnName>>) + '', '' + CONVERT(varchar(100),T2.<<ColumnName>>) + '')'' ' + CHAR(10)
+ CHAR(9) + CHAR(9) + 'ELSE '''' END AS <<ColumnName>>', '<<ColumnName>>', QUOTENAME(COLUMN_NAME)) + NCHAR(10)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Table'
AND COLUMN_NAME NOT IN( 'ID', 'CreateTimeStamp')
FOR XML PATH(''), TYPE).value('./text()[1]', 'nvarchar(max)'), 2, 1, '') + NCHAR(10)
--Add rest of the query
+ 'FROM Table AS T1 ' + NCHAR(10)
+ 'JOIN Table AS T2 ON T1.CreateTimeStamp = T2.CreateTimeStamp ' + NCHAR(10)
+ 'WHERE ID = #ID1 ' + NCHAR(10)
+ 'AND ID = #ID2;'
--PRINT for debugging purposes
PRINT #SQL;
--Execute the dynamic built code
EXECUTE sp_executesql #SQL,
N'#ID1 int, #ID2 int',
#ID1 = 13,
#ID2 = 2006;
The concatenation method is explained on this article.