user: Question: What were the number of sales before 1991?
Columns: ['Year', 'Álbum', 'Charts', 'Sales', 'Certification']
Types: ['real', 'text', 'text', 'real', 'text']
Sample row: [1990.0, 'Xuxa 1', 'No. 1 Latin Charts', 2500000.0, '1x Diamond']
SQL:

assistant: SELECT SUM("Sales") FROM "Table" WHERE "Year" < 1991.0;