liquibase : Insert current date

What you you will have to do is use changelog parameters and
define a “now” or “current_timestamp” parameter that is replaced per database type.

At the top of your <databaseChangeLog>, normally just outside your <changeset>, add per-database definitions of the property like:

  <property name="now" value="sysdate" dbms="oracle"/>
  <property name="now" value="now()" dbms="mysql"/>
  <property name="now" value="now()" dbms="postgresql"/>

then in your changesets use

<column name="Join_date" defaultValueFunction="${now}"/>

Notice the use of defaultValueFunction that will let liquibase know
not to parse it as a date or quote it.