user: Question: What class has less than 12 numbers built operated by Southern?
Columns: ['Class', 'Operator', 'No. Built', 'Year Built', 'Cars per Set', 'Unit nos.']
Types: ['text', 'text', 'real', 'text', 'real', 'text']
Sample row: ['Class 377/1', 'Southern', 64.0, '2002–2003', 4.0, '377101-164']
SQL:

assistant: SELECT "Class" FROM "Table" WHERE "No. Built" < 12.0 AND "Operator" = 'Southern';