This example provides sample configuration for creating a mysql or postgres instance. For Oracle/SQL Servers, replace default values with appropriate values, they are not included in sample since the number of options are high.
If you need to use existing security groups and subnets, remove the sg.tf and subnets.tf files and replace the corresponding sections in main.tf under aws_db_instance
Several parameters are externalized, review the different variables.tf files and change them to fit your needs. Carefully review the CIDR blocks, egress/ingress rules, availability zones that are very specific to your account.