CREATE TABLE table_1231 ("Station" CLOB, "Year opened" CLOB, "Metropolitan borough [c ]" CLOB, "Zone" FLOAT, "Servedby Route maps:- [ dead link ] [ dead link ]" CLOB, "Station users 2006\\u201307" FLOAT, "Station users 2007\\u201308" FLOAT)

What's the biggest zone?
SELECT MAX("Zone") FROM table_1231
SELECT MAX("Zone") FROM "table_1231"