user: Question: What is the surface on 21 June 1993?
Columns: ['Outcome', 'Date', 'Championship', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Winner', '4 August 1986', 'Hilversum', 'Clay', 'Jakob Hlasek', '6–1, 6–3, 6–3']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Date" = '21 June 1993';