SQL & PL/SQL

Hi all,

I am having SQL script like this. First, It will truncate the Temp_emp and then, it will load data from big_table.
Whenever, i run this script from SQL prompt, data inserted into the Temp_emp is doubled. What may be the reason. Am i missing anything
concet of Global Temporary Tables and Truncate ?

*.SQL File starts here*

BEGIN
EXECUTE IMMEDIATE 'TRUNCATE TABLE Temp_emp';
END;
/

INSERT INTO Temp_Temp
SELECT col1,col2,col3,col4,col5
FROM
( SELECT col1,col2,col3,col4,col5 FROM big_table bt
WHERE bt.ROWID IN (SELECT MAX(ROWID) FROM big_table
GROUP BY col1,col2 )
) ;

/

*.SQL File ends here*

Thanks in advance,
Pal