INNER JOIN gets all records that are common between both tables based on the supplied ON clause. LEFT JOIN gets all records from the LEFT linked and the related record from the right table ,but if you have selected some columns from the RIGHT table, if there is no related records, these columns will contain NULL. RIGHT JOIN is like the above but gets all records in the RIGHT table. FULL JOIN ...
By using the merge function and its optional parameters: Inner join: merge(df1, df2) will work for these examples because R automatically joins the frames by common variable names, but you would most likely want to specify merge(df1, df2, by = "CustomerId") to make sure that you were matching on only the fields you desired. You can also use the by.x and by.y parameters if the matching ...
The result of join is always a string, but the object to be joined can be of many types (generators, list, tuples, etc). .join is faster because it allocates memory only once. Better than classical concatenation (see, extended explanation). Once you learn it, it's very comfortable and you can do tricks like this to add parentheses.