UNION
Combines the results of two or more queries into a single result
set that includes all the rows that belong to all queries in the union.
Basic rules for using UNION:
·
The number and the order of the columns must be the same in all
queries.
·
The data types must be compatible
UNION ALL
Incorporates all rows into the results. This includes duplicates.
If not specified, duplicate rows are removed.
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