Merging records in a table and update related tables - sql-server

Question

I have a main table containing users that are linked to various other tables. Sometimes there are duplicates in this main table due to bad imported data and I would like to merge them. See the following tables.
Table: Users
UserID Username FirstName LastName
1 Main John Doe
2 Duplicate John Doo
Table: Records1
RecordID RecordName CreatedUserID UpdatedUserID
1 Test record 1 1 2
2 Test record 2 2 null
3 Test record 3 2 null
CreatedUserID and UpdatedUserID are foreign columns of Users.UserID.
So currently if I want to merge user 1 and 2, I would do it with these SQL statements:
UPDATE Records1 SET UpdatedUserID = 1 WHERE UpdatedUserID = 2
UPDATE Records1 SET CreatedUserID = 1 WHERE CreatedUserID = 2
DELETE FROM Users WHERE UserID = 2
This is just a sample subset but in reality, there are a LOT of related records tables for which I have to add additional SQL-Update statements.
I know I'm probably pushing my luck here, but is there perhaps a way to accomplish the above (update all related tables in a batch and delete the "duplicate" record) rather than updating each foreign field and each related table manually. The users table is basically the base table that links to all other tables so to create individual statements for each table is rather cumbersome so if a shortcut is available, that would be great.

Answer 1

is this helpful.?
Create Table Users(Id int, UserName varchar(10),FirstName varchar(10), LastName Varchar(10))
Create Table Records1(RecordID int, RecordName varchar(20), CreatedUserID int, UpdatedUserID int)
INSERT INTO Users
SELECT 1,'Main','John','Doe' Union All
SELECT 2,'Duplicate','John','Doo' Union All
SELECT 3,'Main3','ABC','MPN' Union All
SELECT 4,'Duplicate','ABC','MPT'
Insert into Records1
SELECT 1,'Test record 1',1,2 Union All
SELECT 2,'Test record 2',2,null Union All
SELECT 3,'Test record 3',2,null Union All
SELECT 1,'Test record 1',3,4 Union All
SELECT 2,'Test record 2',4,null Union All
SELECT 3,'Test record 3',4,null
Select u1.Id as CreatedUserID,U2.id as UpdatedUserID
Into #tmpUsers
from Users u1
JOIN Users u2
--This Conidition Should be changed based on the criteria for identifying Duplicates
on u1.FirstName=u2.FirstName and U2.UserName='Duplicate'
Where u1.UserName<>'Duplicate'
Update r
Set r.UpdatedUserID=u.CreatedUserID
From Records1 r
JOIN #tmpUsers u on r.CreatedUserID=u.CreatedUserID
Update r
Set r.CreatedUserID=u.CreatedUserID
From Records1 r
JOIN #tmpUsers u on r.CreatedUserID=u.UpdatedUserID
Delete from Users Where UserName='Duplicate'
Select * from Users
Select * from Records1
Drop Table #tmpUsers

Answer 2

Since the process of identifying duplicate accounts will be manual then there will (generally) be pairs of accounts to be processed. (I'm assuming that the Inspector can't tick off 15 user accounts as duplicates in your UI and submit the whole lot for processsing.)
A stored procedure like the following may be a good start:
create procedure MergeUsers
#RetainedUserId Int, -- UserId that is being kept.
#VictimUserId Int -- UserId that is to be removed.
as
begin
-- Validate the input.
-- Optional, but you may want some reality checks.
-- (Usernames are probably unique already, eh?)
declare #UsernameMatch as Int, #FirstNameMatch as Int, #LastNameMatch as Int, #EmailMatch as Int;
select
#UsernameMatch = case when R.Username = V.Username then 1 else 0 end,
#FirstNameMatch = case when R.FirstName = V.FirstName then 1 else 0 end,
#LastNameMatch = case when R.LastName = V.LastName then 1 else 0 end,
#EmailMatch = case when R.Email= V.Emailthen 1 else 0 end
from Users as R inner join
Users as V on V.UserId = #VictimUserId and R.UserId = #RetainedUserId;
if #UsernameMatch + #FirstNameMatch + #LastNameMatch + #EmailMatch < 2
begin
-- The following message should be enhanced to provide a better clue as to which user
-- accounts are being processed and what did or didn't match.
RaIsError( 'MergeUsers: The two user accounts should have something in common.', 25, 42 );
return;
end;
-- Update all of the related tables.
-- Using a single pass through each table and updating all of the appropriate columns may improve performance.
-- The case expression will only alter the values which reference the victim user account.
update Records1
set
CreatedUserId = case when CreatedUserId = #VictimId then #RetainedUserId else CreatedUserId end,
UpdatedUserId = case when UpdatedUserId = #VictimId then #RetainedUserId else UpdatedUserId end
where CreatedUserId = #VictimUserId or UpdatedUserId = #VictimUserId;
update Records2
set ...
where ...;
-- Houseclean Users .
delete from Users
where UserId = #VictimUserId;
end;
NB: Left as an exercise is adding try/catch and a transaction in the SP to ensure that the merge is an all or nothing operation.