Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_63 ( rating VARCHAR, rank___number_ VARCHAR, air_date VARCHAR )

### Question ###
What is the rating of the show ranked tba, aired on April 21, 2009?

### Accurate SQL ###

SELECT rating FROM table_name_63 WHERE rank___number_ = "tba" AND air_date = "april 21, 2009"