user: Question: How many grids does dave walker have?
Columns: ['Driver', 'Constructor', 'Laps', 'Time/Retired', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Jackie Stewart', 'Tyrrell - Ford', 95.0, '1:57:59.1', 2.0]
SQL:

assistant: SELECT "Grid" FROM "Table" WHERE "Driver" = 'dave walker';