CREATE TABLE table_203_293 (id DECIMAL, "years of appearance" TEXT, "title" TEXT, "network" TEXT, "character name" TEXT, "actor" TEXT, "notes" TEXT)

what was the last show aired by abc ?
SELECT "title" FROM table_203_293 WHERE "network" = 'abc' ORDER BY "years of appearance" DESC LIMIT 1
SELECT "title" FROM "table_203_293" WHERE "network" = 'abc' ORDER BY "years of appearance" DESC NULLS LAST LIMIT 1