为什么UNION查询在MySQL中这么慢？

When I optimize my 2 single queries to run in less than 0.02 seconds and then UNION them the resulting query takes over 1 second to run. Also, a UNION ALL takes longer than a UNION DISTINCT. I would assume allowing duplicates would make the query run faster and not slower. Am I really just better off running the 2 queries separately? I would prefer to use the UNION.When I optimize my 2 single queries to run in l