dynamically select column name that changed - sql

Question

I have a table as shown below.
ID NAME ADDRESS CITY ROLE Date_Modified
1 Tom something austin manager X
2 Tom nothing austin principal Y
3 Tom anything dallas VP Z
How do write a query to select the column name that have changed between entries 1,2 and 3? Currently I am building a report that needs to identify change. This is what I have so far and need to work with it.
I need to be able to detect via stored proc and see output below.
Id ColumnName DateChanged
2 Address Y
2 Role Y
3 Address Z
3 Role Z

Answer 1

If I understood your question correctly, what you need is detecting changes from one row to another and unpivoting the data. Usage of LAG required SQL Server 2012 or more.
;with cte as (
-- LAG for id is used to skip first row from selection
select id, LAG(id, 1) OVER (ORDER BY id) AS OldId,
address, LAG(address, 1) OVER (ORDER BY id) AS OldAddress,
role, LAG(role, 1) OVER (ORDER BY id) AS OldRole,
Date_Modified
from audit_data
)
SELECT id, ColName, data_col, Date_Modified
FROM
(
select id, address, role, Date_Modified
from cte
-- detect any change in monitored data
where ((OldAddress IS NULL OR address <> OldAddress)
OR (OldRole IS NULL OR role <> OldRole))
AND OldId IS NOT NULL
) AS cp
-- unpivot address and role into data_col column
UNPIVOT
(
data_col FOR ColName IN (address, role)
) AS up;
Data used for setup:
-- drop table audit_data
create table audit_data (
id int,
name VARCHAR(100),
address VARCHAR(100),
city varchar(100),
role VARCHAR(100),
Date_Modified DATETIME2
)
insert into audit_data values (1, 'Tom', 'something', 'austin', 'manager', '20150103'),
(2, 'Tom', 'nothing', 'austin', 'principa', '20150205'),
(3, 'Tom', 'anything', 'dallas', 'VP', '20150314')
go
[Edit] SQL 2008R2 version:
;with ad_cte as (
select id, address, role, Date_Modified, ROW_NUMBER() OVER (ORDER BY id) RowNo
from audit_data
),
cte as (
select ad.id,
ad.address, ad_old.address AS OldAddress,
ad.role, ad_old.role AS OldRole,
ad.Date_Modified
from ad_cte ad
join ad_cte ad_old on ad_old.RowNo + 1 = ad.RowNo
)
SELECT id, ColName, data_col, Date_Modified
FROM
(
select id, address, role, Date_Modified
from cte
-- detect any change in monitored data
where ((OldAddress IS NULL OR address <> OldAddress)
OR (OldRole IS NULL OR role <> OldRole))
-- this should be changed for generality
AND cte.id > 1
) AS cp
-- unpivot address and role into data_col column
UNPIVOT
(
data_col FOR ColName IN (address, role)
) AS up;

Answer 2

This is very similar to Alexei's answer:
CREATE TABLE #temp( ID INT IDENTITY(1, 1),
NAME VARCHAR(30),
ADDRESS VARCHAR(30),
CITY VARCHAR(30),
ROLE VARCHAR(30),
Date_Modified DATETIME );
INSERT INTO #temp
SELECT 'Tom',
'something',
'austin',
'manager',
DATEADD(day, -3, GETDATE())
UNION
SELECT 'Tom',
'nothing',
'austin',
'principal',
DATEADD(day, -2, GETDATE())
UNION
SELECT 'Tom',
'anything',
'dallas',
'VP',
DATEADD(day, -1, GETDATE());
SELECT 'Jon',
'something',
'san antonio',
'assistant manager',
DATEADD(day, -3, GETDATE())
UNION
SELECT 'Jon',
'something',
'austin',
'assistant manager',
DATEADD(day, -2, GETDATE())
UNION
SELECT 'Jon',
'anything',
'dallas',
'manager',
DATEADD(day, -1, GETDATE());
SELECT id,
ColName,
Date_Modified
FROM(
SELECT DISTINCT B.ID,
B.Name,
CASE
WHEN A.ADDRESS <> B.ADDRESS
THEN B.ADDRESS
END AS ADDRESS,
CASE
WHEN A.CITY <> B.CITY
THEN B.CITY
END AS CITY,
CASE
WHEN A.ROLE <> B.ROLE
THEN B.ROLE
END AS ROLE,
B.Date_Modified
FROM(
SELECT *,
ROW_NUMBER() OVER(PARTITION BY NAME ORDER BY Date_Modified DESC) AS ROWNUM
FROM #temp ) AS A
INNER JOIN(
SELECT *,
ROW_NUMBER() OVER(PARTITION BY NAME ORDER BY Date_Modified DESC) AS ROWNUM
FROM #temp ) AS B ON A.NAME = B.NAME
AND CHECKSUM(A.NAME, A.ADDRESS, A.CITY, A.ROLE) <> CHECKSUM(B.NAME, B.ADDRESS, B.CITY, B.ROLE)
AND A.ROWNUM = B.ROWNUM - 1 ) AS cp
UNPIVOT( data FOR ColName IN( address,
role )) AS up;