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_15358729_6 ( average_weekly_rank VARCHAR, average_nightly_rank VARCHAR )

### Question ###
How many were the show's average weekly ranking when it reached No. 2 in average nightly ranking?

### Accurate SQL ###

SELECT COUNT(average_weekly_rank) FROM table_15358729_6 WHERE average_nightly_rank = "No. 2"