Going through tables and replacing IDs resulting from duplicates in dimension table - sql-server

Question

I have a dimension Users table that unfortunately has a bunch of duplicate records. See screenshot.
I have thousands of users and 5 tables referencing the duplicates. I want to delete records with "bad" UserIDs. I want to go through the 5 dependencies and update bad UserIds with "good" (circled in red).
What would be a good approach to this?
Here's what I did to get the above screenshot...
SELECT UserID
,userIds.FirstName
,userIds.LastName
,dupTable.Email
,dupTable.Username
,dupTable.DupCount
FROM dbo.DimUsers AS userIds
LEFT OUTER JOIN
(SELECT FirstName
,LastName
,Email
,UserName
,DupCount
FROM
(SELECT FirstName
,LastName
,UserName
,Email
,COUNT(*) AS DupCount -- we're finding duplications by matches on FirstName,
-- last name, UserName AND Email. All four fields must match
-- to find a dupe. More confidence from this.
FROM dbo.DimUsers
GROUP BY FirstName
,LastName
,UserName
,Email
HAVING COUNT(*) > 1) AS userTable -- any count more than 1 is a dupe
WHERE LastName NOT LIKE 'NULL' -- exclude entries with literally NULL names
AND FirstName NOT LIKE 'NULL'
)AS dupTable
ON dupTable.FirstName = userIds.FirstName -- to get the userIds of dupes, we LEFT JOIN the original table
AND dupTable.LastName = userIds.LastName -- on four fields to increase our confidence
AND dupTable.Email = userIds.Email
AND dupTable.Username = userIds.Username
WHERE DupCount IS NOT NULL -- ignore NULL dupcounts, these are not dupes

Answer 1

This code should work, created for 1 dependency table but you can use the same logic to update other 4 tables.
update t
set UserID = MinUserID.UserID
from
DimUsersChild1 t
inner join DimUsers on DimUsers.UserID = t.UserID
inner join (
select min(UserID) UserID, FirstName, LastName, UserName, Email
from DimUsers
group by
FirstName, LastName, UserName, Email
) MinUserID on
MinUserID.FirstName = DimUsers.FirstName and
MinUserID.LastName = DimUsers.LastName and
MinUserID.UserName = DimUsers.UserName and
MinUserID.Email = DimUsers.Email
select * from DimUsersChild1;
delete t1
from
DimUsers t
inner join DimUsers t1 on t1.FirstName = t.FirstName and
t1.LastName = t.LastName and
t1.UserName = t.UserName and
t1.Email = t.Email
where
t.UserID < t1.UserID
select * from DimUsers;
Here is a working demo