user: Question: What is Years, when Jersey Number(s) is 21, and when Position is SG?
Columns: ['Player', 'Nationality', 'Jersey Number(s)', 'Position', 'Years']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['James Bailey Category:Articles with hCards', 'United States', '20', 'PF / Center', '1979 – 1981']
SQL:

assistant: SELECT "Years" FROM "Table" WHERE "Jersey Number(s)" = '21' AND "Position" = 'SG';