Originally posted by BrianBischof
No linking is necessary. What you are doing is creating two distinct lists of data from two different tables. The UNION keyword then appends the second list to the first list into a virtual table and makes it all appear as one single table. Thus, the number of rows in the new table will be equal to how many rows are in the first SELECT plus how many rows are in the second SELECT.
As a further note, you do have to make very sure that your columns line up, and that the datatypes in your columns are the same. In the case you're working on here, that is pretty trivial. In some other cases, you may have to some data type conversion and/or column aliasing to make everything line up right. If the columns don't line up, SQL chokes (for, I think, fairly obvious reasons).
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