What is the original air date of the episode that had a week ranking of 21?
CREATE TABLE table_23177573_1 (original_air_date VARCHAR, rank__week_ VARCHAR)
SELECT original_air_date FROM table_23177573_1 WHERE rank__week_ = 21
<s>[INST] Write mssql query to answer the following question given the database schema. Schema: CREATE TABLE table_23177573_1 (original_air_date VARCHAR, rank__week_ VARCHAR) Question: What is the original air date of the episode that had a week ranking of 21? [/INST] SELECT original_air_date FROM table_23177573_1 WHERE rank__week_ = 21 </s>