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union vs left join for select
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Chronological Hierarchical 
which query should i be using?

SELECT Name FROM Names WHERE NameID IN (SELECT DISTINCT NameID FROM AllNouns)
UNION
SELECT Name FROM Names WHERE NameID IN (SELECT DISTINCT NameID FROM AllVerbs)

versus

SELECT Name FROM Names WHERE NameID IN (SELECT DISTINCT AllNouns.NameID FROM AllNouns
LEFT JOIN AllVerbs ON
AllNouns.FirstID = AllVerbs.FirstID AND
AllNouns.NameID = AllVerbs.NameID AND
AllNouns.SecondID = AllVerbs.SecondID)