UNION ALL Operator in SQL | Oracle SQL fundamentals

The SQL UNION ALL operator is used to combine the result sets of 2 or more #SELECT statements. It does not remove duplicate #rows between the various SELECT statements (all rows are returned).
Each SELECT statement within the UNION ALL must have the same number of #fields in the result sets with similar data types.
#UNION removes duplicate rows.
#UNIONALL does not remove duplicate rows.