user: Question: What is the league established before 1930 with the Rayo Vallecano club?
Columns: ['Club', 'League', 'Sport', 'Venue', 'Established', 'Capacity']
Types: ['text', 'text', 'text', 'text', 'real', 'real']
Sample row: ['Real Madrid C.F.', 'La Liga', 'Football', 'Santiago Bernabéu', 1902.0, 85454.0]
SQL:

assistant: SELECT "League" FROM "Table" WHERE "Established" < 1930.0 AND "Club" = 'Rayo Vallecano';