Prova così:
codice:select X, Y, Z from tabella INNER JOIN (select X from tabella group by X having count(*) > 20) as tabella2 ON tabella.X = tabella2.X
Prova così:
codice:select X, Y, Z from tabella INNER JOIN (select X from tabella group by X having count(*) > 20) as tabella2 ON tabella.X = tabella2.X