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_20 ( channel_4_weekly_rank_a INTEGER, viewers__millions_ VARCHAR, airdate VARCHAR )

### Question ###
What is the average Channel 4 weekly rank for less than 2.19 million viewers on December 7, 2007?

### Accurate SQL ###

SELECT AVG(channel_4_weekly_rank_a) FROM table_name_20 WHERE viewers__millions_ < 2.19 AND airdate = "december 7, 2007"