user: Question: How many platforms have a Southern opertator and the pattern is All stations via Clapham Junction?
Columns: ['Platform', 'Frequency (per hour)', 'Destination', 'Service Pattern', 'Operator', 'Line']
Types: ['real', 'real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 4.0, 'Highbury & Islington', 'All stations via Shoreditch High Street', 'London Overground', 'East London']
SQL:

assistant: SELECT COUNT("Platform") FROM "Table" WHERE "Operator" = 'Southern' AND "Service Pattern" = 'All stations via Clapham Junction';