user: Question: How many different items appear in the enrollment column that joined in 1931, 1949 1?
Columns: ['Institution', 'Location', 'Nickname', 'Founded', 'Type', 'Enrollment', 'Joined']
Types: ['text', 'text', 'text', 'real', 'text', 'real', 'text']
Sample row: ['George Fox University', 'Newberg, Oregon', 'Bruins', 1885.0, 'Private/Quaker', 3519.0, '1996']
SQL:

assistant: SELECT COUNT("Enrollment") FROM "Table" WHERE "Joined" = '1931, 1949 1';