I got large DB dump file with just one insert query if each row has it's insert command, that's fine I can manage it, but what I should do with one insert for 300K records
that is strange, try to dump it via PhpMyAdmon or BigDump and then export the query as, cvs? not sure, this is weird to me.
Export it using PhpMyAdmin, which comes with cPanel, then import it the same way. Like Pat Gael said, you should probably export it as a CVS.
The one insert record was probably a dump from mysqldump with --extended-insert. This allow you to have faster import when you try to restore the database. Not sure what is the limit of PHPMyAdmin as I don't use it personally, I do believe you can select a database than upload a mysqldump file to import when I used it a few years ago. If you have access to the console, you can login using mysql -u [username] -p; create database [databasename]; use [databasename]; source [path_of_dump_file]; Hope this help.
mysql -uuser -ppass -Ddatabase < sqlstuff.sql I usually import using the above command.. keep in mind phpMyAdmin has a 2MB limit on the sql file.