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 publication ( publication_id number, book_id number, publisher text, publication_date text, price number )
TABLE: CREATE TABLE book ( book_id number, title text, issues number, writer text )

### Question ###
What is the number of distinct publication dates?

### Accurate SQL ###

SELECT COUNT(DISTINCT publication_date) FROM publication