Delete duplicates, and reassign FK value in SQL - sql

Question

I have two tables:
Table1:
[id], [ColA]
Table2:
[id], [Table1Id]
A previous update caused duplicates in Table1 and those duplicates to be assocated with rows in Table2. It looks like this in the db:
Table1
1, 89
2, 89
Table2
6, 1
7, 2
I would like to delete the duplicates and reassign the value of the Table2.Table1Id to the one Table1.id row that should be left. Is this possible in a single statement? Ive seen this post on how to delete all but one, but I am lost on how to reassign the Table2.Table1Id value.
edit:
The end result should look like this:
Table1
2, 89
Table2
6, 2
7, 2

Answer 1

drop table if exists dbo.Table2;
drop table if exists dbo.Table1;
create table dbo.Table1 (
ID int primary key
, ColA int
);
create table dbo.Table2 (
ID int
, Table1ID int
);
alter table dbo.Table2
add constraint FK_Table2_Table1
foreign key (Table1ID)
references dbo.Table1 (ID);
insert into dbo.Table1 (ID, ColA)
values (1, 89), (2, 89);
insert into dbo.Table2 (ID, Table1ID)
values (6, 1), (7, 2);
drop table if exists #temp;
select
ttt.ID
into #temp
from (
select
t.ID
, t.ColA
, ROW_NUMBER() over (order by t.ID) as Rbr
from dbo.Table1 t
inner join (
select
t.ColA
from dbo.Table1 t
group by t.ColA
having COUNT (t.ID) > 1
) tt on t.ColA = tt.ColA
) ttt
where ttt.Rbr > 1
update t2
set
Table1ID = t1i.ID
from #temp t
inner join dbo.Table2 t2 on t.ID = t2.Table1ID
inner join dbo.Table1 t1 on t.ID = t1.ID
inner join dbo.Table1 t1i on t1.ColA = t1i.ColA
and t1i.ID not in (select t.ID from #temp t)
delete t1
from #temp t
inner join dbo.Table1 t1 on t.ID = t1.ID
select
*
from dbo.Table1 t
select
*
from dbo.Table2 t