PostgreSQL new Date Format

The date type is implemented as number of days from 2000-01-01 - and this number has not any visual form - it is just the offset. You can change the visualisation, that is used when the data are visualized.

postgres=# set datestyle to ISO;
postgres=# select current_date;
┌────────────┐
│    date    │
╞════════════╡
│ 2015-11-11 │
└────────────┘
(1 row)

postgres=# set datestyle to GERMAN;
postgres=# select current_date;
┌────────────┐
│    date    │
╞════════════╡
│ 11.11.2015 │
└────────────┘
(1 row)

There are other auxiliary functions for formatting date to_char and processing date string to_date. The set of styles available for datestyle is limited. More datestyle is global variable and using it can increase a risk of unwanted defects in application - so the usage of datestyle is not preferred.

postgres=# select to_char(current_date, 'YYYYMM');
┌─────────┐
│ to_char │
╞═════════╡
│ 201511  │
└─────────┘
(1 row)
set datestyle to iso;
postgres=# select to_date('201511','YYYYMM');
┌────────────┐
│  to_date   │
╞════════════╡
│ 2015-11-01 │
└────────────┘
(1 row)

By default the data are communicated from Postgres to client in text format. So the usage of these formatting functions (functionality) has impact on received data (from database) on client side. to_char does explicit convert to text type, so any client can read it (because it have to be able to read text).