Using OR

Select sex,owner from pet where sex='m' or owner='Diane';

 

using UNION

Select sex,owner from pet where sex='m' union select sex,owner from pet where owner='Diane';

Expected 5 rows to be returned; however, only 4 rows are returned because all duplicate rows are removed.

using union all
Result when the 'all' keyword is used after the 'union' statement:

Select sex,owner from pet where sex='m' union all select sex,owner from pet where owner='Diane';