In Wrangler, you can use either a join or a union to combine multiple datasets.
You can think of a join as a SQL-style join or as an Excel VLOOKUP. Joins allow you to add columns from one dataset into another dataset. This makes your original dataset grow horizontally. People often use joins to add new dimensions to the original data--for example, combining a customers file with a sales file to end up with a file containing sales per customer.
A union allows you to stack multiple datasets on top of each other, adding more rows to your original dataset but keeping the number of columns the same. People often use unions if they are looking to turn multiple small files (for example, sales from January and sales from February) into a single large file.
