Did you read the log? Some of the common "issues" with Merge create specific messages in the log.
At least describe the unexpected results, we can't read your mind.
Or was this post just an excuse to post an advertising link or whatever that dollartree thing is?
MERGE in SAS, especially in a data step, has a very specific meaning and some people use the term "merge" without much detail of what is expected. Merge is a sort of side-by-side combination, typically using one or more variables to match records, to bring variables from multiple sets together.
Limitations on the SAS Merge include but are not limited to:
Only one data set can have multiple observations with the same values of BY variables and get expected results.
Variables with same names that are not used for matching on a BY statement will have only one variable with a value similar to updating data. There are some complexities involved.
Minor differences of values such as leading space " John" vs "John", or case "John" "JohN" are not equal and records won't match.
And sometimes people want to APPEND data, stack vertically, but use MERGE because of not being familiar with the difference in SAS.
So code of what was attempted and a clear description of what was expected are important to answer this sort of question. Example data is the best way to provide start data, expected and actual results.