If you get an error saying:
Merging transformations failed: Cannot merge mapping from <table_name>.
It means that you are loading two different tables into one object in one workspace.
How to understand this
Important thing to remember is that all transformations in one bucket and in one phase are executed in one environment.
And if you say in one transformation that table A should be loaded into SQL table called "table_one" and in a second transformation that table B should be loaded into SQL table called "table_one", it is not clear what should be in the table "table one" in the end. That's why you will get the above specified error.
Tip: If you check the error message, it will show you which transformations' input mapping you should check.