Union and Union All are very similar, but if you don’t understand the differences, it can cause trouble.
In this video I do a quick demonstration of the Union and Union All Function.
Video: SQL Server Union and Union All
How to use the SQL Server Union and Union All Operators to combine data sets.
I use the Wide World Importers and the following scripts:
select * from [Application].[People] where PersonID between 1 and 5 union select * from [Application].[People] where PersonID between 4 and 9
See the original SQL Union and Union All video.