CREATE TABLE table_name_63 (rating VARCHAR, rank___number_ VARCHAR, air_date VARCHAR)

What is the rating of the show ranked tba, aired on April 21, 2009?
SELECT rating FROM table_name_63 WHERE rank___number_ = "tba" AND air_date = "april 21, 2009"
SELECT "rating" FROM "table_name_63" WHERE "air_date" = "april 21, 2009" AND "rank___number_" = "tba"