To generate the backup of mysql database using cron job refer following three format as per your requirement.
1) Cron job to generate database backup in .sql format
* * * * * /usr/bin/mysqldump -u databaseusername databasename -ppassword > /path of database database.sql
2) Cronjob to compress database backup in .bz2 format
* * * * * /usr/bin/mysqldump -u datbaseusername databasename -pdatbasepassword|bzip2 -c > /path of database database.bz2
3) Cronjob to compress database backup in .gz format
* * * * * /usr/bin/mysqldump -u databaseusername databasename -ppassword|gzip > /path of databasedatabase.gz
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