in reply to adding database values to csv file

Most databases offer functionality to allow you to dump the contents in various formats. Maybe you can make use of those tools? They typically give good performance.

Depending on the database brand it might be possible to use a SQL statement to produce a csv formatted output file, e.g. something like (mySQL):

SELECT col1, col2, col3, ... FROM some_table INTO OUTFILE '/tmp/some_table.csv' FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n'