How many different original air dates does the episode with series number 13 have?
CREATE TABLE table_19236587_4 (original_air_date VARCHAR, series_no VARCHAR)
SELECT COUNT(original_air_date) FROM table_19236587_4 WHERE series_no = 13
<s>[INST] Write mssql query to answer the following question given the database schema. Schema: CREATE TABLE table_19236587_4 (original_air_date VARCHAR, series_no VARCHAR) Question: How many different original air dates does the episode with series number 13 have? [/INST] SELECT COUNT(original_air_date) FROM table_19236587_4 WHERE series_no = 13 </s>