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_66 ( population_2006_census INTEGER, local_government_area VARCHAR, rank VARCHAR )

### Question ###
What was the 2006 population for the local government area of alexandrina council whose rank was smaller than 19?

### Accurate SQL ###

SELECT AVG(population_2006_census) FROM table_name_66 WHERE local_government_area = "alexandrina council" AND rank < 19