What is the difference between UNION and UNION ALL?

Question

What is the difference between UNION and UNION ALL?

Answer 1

UNION ALL also works on more data types as well. For example when trying to union spatial data types. For example:

select a.SHAPE from tableA a
union
select b.SHAPE from tableB b

will throw

The data type geometry cannot be used as an operand to the UNION, INTERSECT or EXCEPT operators because it is not comparable.

However union all will not.