CREATE TABLE table_203_197 (id DECIMAL, "#" DECIMAL, "title" TEXT, "artist" TEXT, "highest pos. reached" DECIMAL, "weeks at no. 1" TEXT)

who had the most weeks at number one , according to the table ?
SELECT "artist" FROM table_203_197 ORDER BY "weeks at no. 1" DESC LIMIT 1
SELECT "artist" FROM "table_203_197" ORDER BY "weeks at no. 1" DESC NULLS LAST LIMIT 1