Sql Excel : UNION ALL

UNION ALL is a set operation that combines all rows in two tables, by just creating a
result set with all the rows from each input table. The columns must be the same
in each of the input tables. In practice, this means that UNION ALL almost always
operates on subqueries, because it is unusual for two tables to have exactly the
same columns.
SQL has other set operations, such as UNION, INTERSECTION, and MINUS (also called
EXCEPT). The UNION operation combines the rows in two tables together, and then
removes duplicates. This means that UNION is much less efficient than UNION ALL,
so it is worth avoiding. INTERSECTION takes the overlap of two tables—rows that are
in both. However, it is often more interesting to understand the relationship
between two tables—how many items are in both and how many are in each one
but not the other.