diffrenet output between select statement and exp/imp

in Oracle 11.2.0.3

CREATE TABLE A

(

  LETTER                     VARCHAR2(2 BYTE)   NOT NULL,

  MINOR_VERSION              NUMBER(2)          NOT NULL,

  PATCH_VERSION              VARCHAR2(10 BYTE)

)

LOGGING

NOCOMPRESS

NOCACHE

NOPARALLEL

MONITORING;

 

insert into a values ('D',4,null);

 

alter table a add

(

    MIGRATION_IN_PROGRESS_BOO       VARCHAR2(1) DEFAULT 'F' not null

);

 

 

alter table a modify

(

    MIGRATION_IN_PROGRESS_BOO       DEFAULT null

);

 

If I perform a “select * from a;” i would get: 'D',4,null, ‘F’

However, if I export and import the table you i get: 'D',4,null, null

The export itself extracts the “null”.

 

If you perform an update on source table of column MIGRATION_IN_PROGRESS_BOO=’F’, then exp/imp are ok.