This brick is used to combine two datasets into a single one.
After connecting two datasets to brick's inputs, you must specify what kind of union you need.
Vertically means two datasets are stacked "one top of each other", the brick checks whether the column names and types match and are in the same order in both datasets.
Horizontally means two datasets are stacked "side by side", the brick checks whether the number of rows is the datasets are the same. If there are columns with the same name, corresponding columns will get "_x" and "_y" suffixes.
Be mindful of the column names when doing horizontal union. If the column repeats twice, better remove it prior to the union.
Be mindful of the order of the data, as the brick unites data as-is.