setting datestyle

Way 1 : setting datestyle Per Database Only

show datestyle; show you current date style "ISO, DMY" or "ISO, MDY"

Now depending on what you want in postgres DMY or MDY set in below query

ALTER DATABASE "my_database_name" SET datestyle TO "ISO, DMY";

or

ALTER DATABASE "my_database_name" SET datestyle TO "ISO, MDY";

Most important step : Always after setting datestyle restart postgres

sudo service postgresql restart

Or

sudo /etc/init.d/postgresql restart

Lets test configuration

if you have set DMY below query should work for you

Query:select '20/12/2016'::date Output: "2016-12-20"

Or

if you have set MDY below query should work for you

Query:select '12/19/2016'::date Output: "2016-12-19"

Way 2 : Permanently : whatever you set in config file will be set in all databases you will create in future

In /etc/postgresql/9.3/main/postgresql.conf set

datestyle = 'iso, dmy' OR datestyle = 'iso, mdy'

Most important step : Always after setting datestyle restart postgres

sudo service postgresql restart

Or

sudo /etc/init.d/postgresql restart

Lets test configuration

if you have set DMY below query should work for you

Query:select '20/12/2016'::date Output: "2016-12-20"

Or

if you have set MDY below query should work for you

Query:select '12/19/2016'::date Output: "2016-12-19"