user: Question: How many years had the best actress in a revival category?
Columns: ['Year', 'Award', 'Category', 'Nominated work', 'Result']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1984.0, 'Olivier Award', 'Best Actress in a Revival', 'Measure for Measure', 'Nominated']
SQL:

assistant: SELECT COUNT("Year") FROM "Table" WHERE "Category" = 'best actress in a revival';