Check z-ocsinventory-server.conf, it is at /etc/httpd/conf.d/z-ocsinventory-server.conf on CentOS :
# Master Database settings
# Replace localhost by hostname or ip of MySQL server for WRITE
PerlSetEnv OCS_DB_HOST localhost
# Replace 3306 by port where running MySQL server, generally 3306
PerlSetEnv OCS_DB_PORT 3306
# Name of database
PerlSetEnv OCS_DB_NAME ocsweb
PerlSetEnv OCS_DB_LOCAL ocsweb
# User allowed to connect to database
PerlSetEnv OCS_DB_USER DATABASE_USER (maybe root ?)
# Password for user
PerlSetVar OCS_DB_PWD DATABASE_PASSWORD
Restart apache server