CREATE TABLE table_26815 ("Episode no." FLOAT, "Airdate" CLOB, "Viewers" FLOAT, "BBC Three weekly ranking" CLOB, "Cable rank" CLOB)

What date did the episode air that had a ranking of 17 for cable?
SELECT "Airdate" FROM table_26815 WHERE "Cable rank" = '17'
SELECT "Airdate" FROM "table_26815" WHERE "Cable rank" = '17'