How many episodes  of 30 minutes were written by John Sullivan?
CREATE TABLE table_17641206_4 (duration VARCHAR, written_by VARCHAR)
SELECT COUNT(duration) FROM table_17641206_4 WHERE written_by = "John Sullivan"
<s>[INST] Write mssql query to answer the following question given the database schema. Schema: CREATE TABLE table_17641206_4 (duration VARCHAR, written_by VARCHAR) Question: How many episodes  of 30 minutes were written by John Sullivan? [/INST] SELECT COUNT(duration) FROM table_17641206_4 WHERE written_by = "John Sullivan" </s>