Dear Alan,
Was the problem due to not padding the data before inserting into the
dump file(D:\TEMP\dump.txt) ?
Remember my dump file size was 3 GB.
I have not casted while inserting into table i have just removed null
chars. i.e. '\0'
I successfully attached that dump file as EXTERNAL TABLE i.e. TEMP1
but when i executed command this:

INSERT INTO REALTABLE SELECT COL1,COL2 FROM TEMP1

then it started inserting data into database but after inserting for 5
minutes it says:
I/O error for file fseek "D:\TEMP\dump.txt" Error while trying to open
file.
I have no idea why the error is coming...

Please help me