user: Question: Who is the opponent in the final when Frankfurt is championship and the year is less than 1993.0?
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Opponent in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Winner', 1991.0, 'Frankfurt', 'Carpet (i)', 'Jim Courier', '3–6, 7–6 (7–5) , 6–3, 6–4']
SQL:

assistant: SELECT "Opponent in the final" FROM "Table" WHERE "Championship" = 'Frankfurt' AND "Year" < 1993.0;