Question

I have the following file name changing log table.

ChangeNameLog(Date, OldName, NewName)
Primary key: Date, OldName

The data of the table looks like

Date OldName NewName 
1/1  aaa     bbb
1/2  bbb     ccc
1/3  ccc     bbb
1/4  bbb     ddd
2/1  xx      yy
2/2  yy      zz

(The file name aaa was changed to bbb, and then to ccc, bbb, ddd later
The file name xx was changed to yy, and then to zz)

I want to get the oldest name for all the new names. The result will look like

Date NewName OldestName
1/2  bbb     aaa
1/3  ccc     aaa
1/4  ddd     aaa
2/1  yy      xx
2/2  zz      xx

Is anyway to write a Transact-SQL (Version 2008 is fine) without using cursor to loop the logging table?

The following SQL can be used to prepare the data.

declare @log table (
    Date Date, OldName varchar(20), NewName varchar(20) not null 
    primary key (Date, OldName)
);
-- The real table also have the following CK
-- create unique index IX_CK on @log (Date, NewName)

insert into @log values
 ('2012-01-01', 'aaa', 'bbb')
,('2012-01-02', 'bbb', 'ccc')
,('2012-01-03', 'ccc', 'bbb')
,('2012-01-04', 'bbb', 'ddd')
,('2012-01-05', 'ddd', 'eee')

,('2012-01-03', 'xx',  'yy')
,('2012-02-02', 'yy',  'zz')
,('2012-02-03', 'zz',  'xx')
;

Answer 1

My own solution:

declare @log table (
    Date Date, OldName varchar(20), NewName varchar(20) 
    primary key (Date, OldName)
);

insert into @log values
 ('2012-01-01', 'aaa', 'bbb')
,('2012-01-02', 'bbb', 'ccc')
,('2012-01-03', 'ccc', 'bbb')
,('2012-01-04', 'bbb', 'ddd')
,('2012-01-05', 'ddd', 'eee')

,('2012-01-03', 'xx',  'yy')
,('2012-02-02', 'yy',  'zz')
,('2012-02-03', 'zz',  'xx')
;

;with m as (
    select Date, OldName, NewName, 1 as L
    from @log 
    union all
    select l.Date, m.OldName, l.NewName, L + 1
    from @log l join m on l.Date > m.Date and l.OldName = m.NewName
)
select * 
from m
where L = (select MAX(l) from m m1 where NewName = m.NewName and Date = m.Date)
order by 1

Output:
The following result shows that the two original names are aaa and xx.

Date       Orig Name L
2012-01-01  aaa bbb 1
2012-01-02  aaa ccc 2
2012-01-03  aaa bbb 3
2012-01-03  xx  yy  1
2012-01-04  aaa ddd 4
2012-01-05  aaa eee 5
2012-02-02  xx  zz  2
2012-02-03  xx  xx  3