Cannot convert type date to integer using liquibase

Question

I'm trying to change date type in my Postgsql DB to integer one using this changeset:

--changeset Sihem:001
ALTER TABLE training 
  ALTER COLUMN end_date TYPE integer USING end_date::integer; 

But I got an error: could not convert type date to integer. Any idea please?

Answer 1

You can't. However, you could convert to, say, a number of days since some base date:

using extract(epoch from (end_date - '1970-01-01'::date))

Answer 2

I resolve it by:

 ALTER TABLE training
    ALTER COLUMN end_date TYPE integer USING (EXTRACT(ISOYEAR FROM end_date));