Thanks for the response.

Note: the main difference between simply using a comma (1) or union all (2) is visualisation of the resulting table, i.e.

(1) present all four columns from the two resultnig tables side by side (= resulting table with 4 columns and 1 row), while

(2) presents results from one table in one column and results from the second result table in a second column (= resulting table with two columns and two rows).