Migrate tables from MS Access to MS SQL Server [duplicate] - sql-server

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Migration Access to SQL server 2012
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I'm moving a database from MS Access to MS SQL Server 2012. My question involves a data issue we need to resolve for the SQL Server database. We have a main MS Access table that generates an integer key then used in several other tables. In Access, the column autoincrements when a new record is created. The issue we're having is that there are gaps in the Access tables columny where records were (unwisely) deleted. It seems that the solution for the SQL Server version of he table is to migrate the table with that column set as PRIMARY and UNIQUE, without using the IDENTITY value. That means we would no longer get an autoincremented number. We'd have to write some code to create that numbering using a SELECT with MAX(). Is there a better way to resolve this issue?

Answer 1

You have TableA that currently maintains the Primary Key that is used is related tables. You want TableB to now control the creation of this Primary Key. I don't see why you can't continue using an auto-incrementing primary key on TableB to manage the creation of the Primary Key. It doesn't matter that previous values have gaps. SQL Server has a way around that.
You can't convert an exiting column in a table to IDENTITY, but you can create a table in SQL Server with an IDENTITY column, turn the IDENTITY function off, populate it with your own values (gaps and all), and then turn the IDENTITY function back on.
From the documentation on IDENTITY_INSERT:
-- Create products table.
CREATE TABLE products (id int IDENTITY PRIMARY KEY, product varchar(40))
GO
-- Inserting values into products table.
INSERT INTO products (product) VALUES ('screwdriver')
INSERT INTO products (product) VALUES ('hammer')
INSERT INTO products (product) VALUES ('saw')
INSERT INTO products (product) VALUES ('shovel')
GO
-- Create a gap in the identity values.
DELETE products
WHERE product = 'saw'
GO
SELECT *
FROM products
GO
-- Attempt to insert an explicit ID value of 3;
-- should return a warning.
INSERT INTO products (id, product) VALUES(3, 'garden shovel')
GO
-- SET IDENTITY_INSERT to ON.
SET IDENTITY_INSERT products ON
GO
-- Attempt to insert an explicit ID value of 3
INSERT INTO products (id, product) VALUES(3, 'garden shovel').
GO
-- SET IDENTITY_INSERT to OFF.
SET IDENTITY_INSERT products OFF
GO
SELECT *
FROM products
Using this technique, you can convert the Access version of TableB to temp_TableB in SQL Server, where there is no identity column. Then create a real TableB in SQL Server with an IDENTITY column.
Then you could
SET IDENTITY_INSERT TableB ON
INSERT INTO TableB ( {columnlist} )
SELECT * from temp_TableB
SET IDENTITY_INSERT TableB OFF
Now you have TableB populated correctly and ready to create the next auto-incremented IDENTITY value.