TIMESTAMP with T as separator (ISO 8601)

You can specify a format when you insert data to a table or select data from a table.

Example:

dbadmin=> create table t1 (c1 timestamp);
CREATE TABLE

dbadmin=> insert into t1 values (to_timestamp('2004-10-19T10:23:54', 'yyyy-mm-dd HH24:mi:ss'));
 OUTPUT
--------
      1
(1 row)

dbadmin=> commit;
COMMIT

dbadmin=> select * from t1;
         c1         
---------------------
 2004-10-19 10:23:54
(1 row)

dbadmin=> select to_char(c1, 'yyyy-mm-ddThh24:mi:ss') from t1;
       to_char      
---------------------
 2004-10-19T10:23:54

(1 row)