user: Question: How many values for joined occur at Guilford College?
Columns: ['Institution', 'Location', 'Nickname', 'Founded', 'Type', 'Enrollment', 'Football?', 'Joined']
Types: ['text', 'text', 'text', 'real', 'text', 'real', 'text', 'real']
Sample row: ['Bridgewater College', 'Bridgewater, Virginia', 'Eagles', 1880.0, 'Private', 1690.0, 'Yes', 1976.0]
SQL:

assistant: SELECT COUNT("Joined") FROM "Table" WHERE "Institution" = 'Guilford College';