Question

What is the output behavior difference between UNION and UNION ALL when combining two SELECT queries that happen to return some identical rows?

A UNION removes duplicate rows from the combined result; UNION ALL keeps all rows including duplicates
B UNION ALL removes duplicates; UNION keeps them
C Both behave identically in all SQL implementations
D UNION requires both queries to return the same number of rows
E UNION ALL is not valid ANSI SQL syntax
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