MS SQL split old table into many to many relation - sql

Question

I have an old table with lots of columns that i want to split into 3 tables with many to many relation.
The old table have no identity column.
Old table:
CustomerNumber
FirstName
LastName
Address
Postal
City
....
New tables
Customer:
Id
Customernumber
Firstname
Lastname
... ect
Address:
Id
Address
Postal
City
... ect
CustomerAddress
Id
CustomerId
AddressId
Now how can I spilt the old tabel into the new ones using SQL?
I have tried with MERGE but that can't handle more than one table at the time. One option is using CURSOR, but I read that it is a bad idea, to use that or iteration, but for now that is the only solution I have found for this.
declare
#CustomerId bigint,
#CustomerNumber float,
#Status int,
#Address varchar(50),
#RoadNumber int,
#LastEdited datetime,
#AddressId bigint
declare my_cursor cursor
local static read_only forward_only
for
select CustomerNumber, Address, Housenumber, Status, Date
from [db1].dbo.OldCustomer k
where
FIRMANR in (1, 40, 60, 80, 90, 120, 180, 400)
open my_cursor
fetch next from my_cursor into #CustomerNumber, #Address, #RoadNumber, #Status, #LastEdited
while ##FETCH_STATUS = 0
begin
--if the customer already exists we get the identity
if exists (select Id from [db2].dbo.Customers where CustomerNumber = #CustomerNumber)
select #CustomerId = Id from [db2].dbo.Customers where CustomerNumber = #CustomerNumber
--if the customer does not exit we need to insert and retrieve the new Identity value
else
begin
-- insert the customer
insert into [db2].dbo.Customers (CustomerNumber, [Status], LastEdited) values (#CustomerNumber, #Status, #LastEdited)
set #CustomerId = SCOPE_IDENTITY()
end
-- get address if it already exists
if exists (select Id from [db2].dbo.Addresses where Road = #Address and Roadnumber = #RoadNumber)
select #AddressId = Id from [db2].dbo.Addresses where Road = #Address and Roadnumber = #RoadNumber
else
begin
-- insert new addresses
insert into [db2].dbo.Addresses (Road,Roadnumber) values (#Address, #RoadNumber)
set #AddressId = SCOPE_IDENTITY()
end
-- insert customer => address reference if it does not exist
if not exists (select Id from [db2].dbo.CustomerAddress where CustomerId = #CustomerId and AddressId = #AddressId)
-- insert customer => address reference
insert into [db2].dbo.CustomerAddress(CustomerId,AddressId) values (#CustomerId, #AddressId)
fetch next from my_cursor into #CustomerNumber, #Address, #RoadNumber, #Status, #LastEdited
end
close my_cursor
deallocate my_cursor

Answer 1

It would probably be easiest to:
Add a column to old customer called AddressId
Populate it with unique IDs (you can reuse the Customer ID, or if its GUID, use NewID())
Create new tables for address and customeraddress
Insert part of the old customer data into each new table
Drop columns from Customer that relate to address
--populate new Address table
INSERT INTO Address(id,col1,col2...)
SELECT AddressID, col1, col2... FROM Customer
--populate new CustomerAddress table
INSERT INTO CustomerAddress(CustomerId,AddressId)
SELECT Id, AddressID FROM Customer
With SQLS you can do this as a simple script, with a transaction if you want.. No need for stored procedures, cursors, merge etc..
Don't give CustomerAddress its own Id column; the primary key of CustomerAddress is the combination of CustomerId and AddressId; make a composite PK, not a separate one
Tbh, I'd probably not have a CustomerAddress table and instead just have a BillingAddressId, WorkAddressId, HomeAddressId, ShippingAddressId column in customer, but it's up to you how to manage this; If you have lots and variable types of addresses then sure, have a M:M breakdown, but if realistically your customers are only ever going to have up to 3 addresses etc, I'd stick with having a named column stating what the address was for, in customer
If you do go with a CustomerAddress table, consider adding a column declaring the type/reason for the address