TABLE_EXISTS_ACTION

Those who are familiar with oracle data pump may know very well about TABLE_EXISTS_ACTION import (impdp) parameter.

TABLE_EXISTS_ACTION = {SKIP | APPEND | TRUNCATE | REPLACE}

This parameter is used when you import a table which is already exists in import schema. The default value is 'SKIP', so if you not use this parameter and impdp found that the table which to be imported is already exist then impdp skip this table from import list.

Now you may interested about rest of the three values-

APPEND - The import will be done if the table does not have any Primary key or Unique key constraints. If such constraint exists then you need to ensure that append operation does not violate Primary key or Unique key constraints (that means it does not occur data duplication).

TRUNCATE - If the table is not a parent table ( i.e, No other table references it by creating foreign key constraint) then it truncate the existing data and load data from dump file. Otherwise data will not be loaded.

REPLACE - This is the most tricky value of TABLE_EXISTS_ACTION parameter. If the importing table is a parent table ( i.e, other table references it by creating foreign key constraint ) then the foreign key will be deleted from child table. All existing data will be replaced with imported data.