Generally SAS data sets are combined either vertically or horizontally.
When combined vertically, you concatenate the data sets one after another, or you interleave observations from the data sets in order by one or more variables. Observations are not combined side-by-side horizontally nor are they overlaid.
When combined horizontally, you usually match data sets by the values of key variables in common or by programmatically aligning observations when they do not have variables in common. The observations in the data sets can be aligned side-by-side and data in one data set can be overlaid by data from another.
You can use these methods to combine SAS data sets vertically: