Comparing Sets of Data in T-SQL

Louis Davidson figured out which of these was not like the others, which of these just didn’t belong:

There are many occasions when we want to see the differences between two sets of data. Sometimes a whole table, a subset of a table, or even the results from a couple of queries, like in a unit test.

Maybe you want to see that two sets are exactly the same, for example domain table in DEV, PROD, or maybe even from source control. You might you have a orders table and an orders_history table and you want to see the overlap/changes over a given period of time, like for example, to clean out any useless history.

No matter what the reason, there is a query pattern that will work for you. In this blog I will demonstrate several of these techniques and why you might want to use them in different places.

Click through for those techniques. I am particularly fond of INTERSECT/EXCEPT because of how it handles missing data and typically performs quite well.