I need to use the default value of batch timestamp in my DDL ,does it exists? or i can mark low date to my start date column?
The default 'default value' used by the DBMS is NULL.
For some data types you can specify DEFAULT and the dbms will supply a value (numeric data types default to 0, characters default to spaces) but not for DATE or TIMESTAMP columns. For thos data types you have to specify a default value in your DDL.For instance:
CREATE TABLE t1 ( ... ,LOAD_TS TIMESTAMP(0) NOT NULL DEFAULT TIMESTAMP'2000-01-01 00:00:00' ... );