Query to Get All IDs When Duplicate Data Has Different Keys - sql

Question

I've got a SQL table similar to this:
+-----------------------------------------------+
| ID | FirstName | LastName | SomeOtherData|
+-----------------------------------------------+
| 200 | Robert | Barone | Foo |
| 228 | Doug | Heffernan | Bar |
| 2091 | Robert | Barone | Foo |
| 3921 | Doug | Heffernan | Bar |
| 291 | Greg | Warner | Barfoo |
+-----------------------------------------------+
Now what I'm having trouble producing is a table that'll list both IDs for a given Person, assuming that FirstName and LastName are used to indicate duplicates. So, basically I'm trying to get:
+---------------------------------------------------------+
| ID | OtherID | FirstName | LastName | SomeOtherData|
+---------------------------------------------------------+
| 200 | 2091 | Robert | Barone | Foo |
| 228 | 3921 | Doug | Heffernan | Bar |
| 291 | | Greg | Warner | Barfoo |
+---------------------------------------------------------+
Would anyone be able to help me out with something like this? Thanks!

Answer 1

You can use a PIVOT which will transform the data from rows into columns:
select [1] Id,
[2] OtherId,
firstname,
lastname
from
(
select id, firstname, lastname,
row_number() over(partition by firstname, lastname
order by id) rn
from yourtable
) src
pivot
(
max(id)
for rn in ([1], [2])
) piv
See SQL Fiddle with Demo
Or you could use an aggregate function with a CASE expression:
select
max(case when rn = 1 then id end) Id,
max(case when rn = 2 then id end) OtherId,
firstname,
lastname
from
(
select id, firstname, lastname,
row_number() over(partition by firstname, lastname
order by id) rn
from yourtable
) src
group by firstname, lastname
The above will work great if you have a known number of duplicate values (1, 2, etc). You could also implement dynamic SQL if you have more than 2 id's. The dynamic SQL would look like:
DECLARE #cols AS NVARCHAR(MAX),
#colNames AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' + QUOTENAME(cast(row_number() over(partition by firstname, lastname order by id) as varchar(50)))
from yourtable
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
select #colNames = STUFF((SELECT distinct ', ' + QUOTENAME(cast(row_number() over(partition by firstname, lastname order by id) as varchar(50))) +' as Id_' + cast(row_number() over(partition by firstname, lastname order by id) as varchar(50))
from yourtable
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT ' + #colNames + ', firstname, lastname from
(
select id, firstname, lastname,
row_number() over(partition by firstname, lastname
order by id) rn
from yourtable
) x
pivot
(
max(id)
for rn in (' + #cols + ')
) p
'
execute(#query)
See SQL Fiddle with Demo
The result of all 3 would be:
| ID | OTHERID | FIRSTNAME | LASTNAME |
-----------------------------------------
| 200 | 2091 | Robert | Barone |
| 228 | 3921 | Doug | Heffernan |
| 291 | (null) | Greg | Warner |