user: Question: How many entries are shown for date of successors formal installation where successor is John W. Walker (DR)?
Columns: ['State (class)', 'Vacator', 'Reason for change', 'Successor', 'Date of successors formal installation']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Alabama (2)', 'New seats', 'Alabama was admitted to the Union.', 'John W. Walker (DR)', 'Elected December 14, 1819']
SQL:

assistant: SELECT COUNT("Date of successors formal installation") FROM "Table" WHERE "Successor" = 'John W. Walker (DR)';