CREATE TABLE table_20263 ("Platform" FLOAT, "Frequency  ( per hour ) " FLOAT, "Destination" TEXT, "Service Pattern" TEXT, "Operator" TEXT, "Line" TEXT)

How many platforms have a southern opertator and the pattern is all stations via clapham junction?
SELECT COUNT("Platform") FROM table_20263 WHERE "Operator" = 'Southern' AND "Service Pattern" = 'All stations via Clapham Junction'
SELECT COUNT("Platform") FROM "table_20263" WHERE "Operator" = 'Southern' AND "Service Pattern" = 'All stations via Clapham Junction'