user: Question: On how many different dates did schools from Chestnut Hill, Massachusetts join the conference?
Columns: ['Institution', 'Location', 'Nickname', 'Founded', 'Type', 'Enrollment', 'Joined']
Types: ['text', 'text', 'text', 'real', 'text', 'real', 'real']
Sample row: ['Agnes Scott College †', 'Decatur, Georgia', 'Scottish Terriers', 1889.0, 'Private/Presbyterian', 914.0, 2002.0]
SQL:

assistant: SELECT COUNT("Joined") FROM "Table" WHERE "Location" = 'Chestnut Hill, Massachusetts';