SQL Update Parent ID from Same table

Question

Is it possible to update self referencing parent id with Update From query.

Tables I have

Acc

AccID    Name  ParentAccID  AccNumber
01       A       Null        A001
02       B       Null        A002   
03       C       Null        A003
04       D       Null        A004
05       E       Null        A005

AccRef

AccNumber       MasterAcc    Name
A001             A001         A
A002                          B 
A003             A002         C
A004             A005         D 
A005             A009         E

the way it should be joined is with AccNumber and then need to updat AccID in ParentAccID based on MasterAcc of that Acc. Only for existing AccNumber and if AccNumber and MasterAcc is not same (sorry if its big confusing)

Result table should look like

Acc

AccID    Name  ParentAccID  AccNumber
01       A       Null        A001
02       B       Null        A002   
03       C       02          A003
04       D       05          A004
05       E       Null        A005

Thanks

Answer 1

Try this,

DECLARE @Acc Table (AccID varchar(10),Name  varchar(200),ParentAccID  varchar(200), AccNumber varchar(200))
Insert into @Acc Values 
('01','A',Null,'A001'),
('02','B',Null,'A002'),   
('03','C',Null,'A003'),
('04','D',Null,'A004'),
('05','E',Null,'A005')

DECLARE @AccRef Table (AccNumber varchar(10),MasterAcc varchar(200),Name  varchar(200))
Insert into @AccRef Values 
('A001','A001','A'),
('A002',Null,'B'), 
('A003','A002','C'),
('A004','A005','D'), 
('A005','A009','E')

Update A set ParentAccID = M.AccID From @Acc A
Inner Join @AccRef R on R.AccNumber = A.AccNumber and R.AccNumber <> R.MasterAcc
Inner Join @Acc M on M.AccNumber = R.MasterAcc 

Hope this is what you are looking for.

Finally,

Select * from @Acc