Question

I am looking for an efficient way to compare data between an Oracle and SQL Server table. I have no control over the Oracle table and can only perform select queries. This table contains 30,000+ rows. Currently I create a data set from the Oracle table and then compare the data with a SQL Server table that I do maintain. In this case I am just checking for the presence of a student number in the SQL Server table. In cases where the number is not present, I insert it into the SQL Server table. This is, as you can imagine, horribly inefficient. Your suggestions and examples would be greatly appreciated.

Answer 1

Create a Linked Server instance on SQL Server, using an account that has access on the Oracle instance.

Then, you can update the SQL Server table with the missing contents using:

INSERT INTO [SQLServer].[dbo].[table]
SELECT columns
  FROM [Oracle].[database].[schema].[table] x
 WHERE NOT EXISTS(SELECT NULL
                    FROM [SQLServer].[dbo].[table] y
                   WHERE y.student_number = x.student_number)

There are NOT IN and LEFT JOIN/IS NULL alternatives — NOT IN and NOT EXISTS perform better than LEFT JOIN/IS NULL when the columns compared (in this case, student_number) is not nullable (the value can never be NULL).

It’s easy to script this as a SQL Server Agent Job if you need it to run periodically.