user: Question: What is the lowest goal difference of club real betis, who has less than 18 wins?
Columns: ['Position', 'Club', 'Played', 'Points', 'Wins', 'Draws', 'Losses', 'Goals for', 'Goals against', 'Goal Difference']
Types: ['real', 'text', 'real', 'real', 'real', 'real', 'real', 'real', 'real', 'real']
Sample row: [1.0, 'Real Betis', 34.0, 42.0, 18.0, 6.0, 10.0, 66.0, 42.0, 24.0]
SQL:

assistant: SELECT MIN("Goal Difference") FROM "Table" WHERE "Club" = 'real betis' AND "Wins" < 18.0;