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_203_645 ( id number, "lower mississippi periods" text, "lower yazoo phases" text, "lower yazoo\ndates" text, "tensas/natchez phases" text, "cahokia phases" text, "cahokia dates" text, "ohio/miss. river\nconfluence phases" text, "ohio/miss. dates" text )

### Question ###
how many cahokia phases were there ?

### Accurate SQL ###

SELECT COUNT(DISTINCT "cahokia phases") FROM table_203_645