To design multi-tenant application, you have some options for database design
1.Separate Database: which is the most easy but resource consuming, MySQL will fit in this design but for every tenant you will need new Database. This will be easier for administration, operation activities like backup and restore and will give you complete isolation of the customer data.
2.Shared Database, Separate Schemas: In this approach one database server is used but for every new tenant you need to create new schema. MySQL doesn't support this. Alternative DBMS is PostgreSQL. This solution achieve best resource utilisation and operation activities like backup and restore could be handled as well.
3.Shared Database, Shared Schema: as explained by onurozgurozkan you need to store tenant id in each record since it is shared schema. This approach is supported by MySQL and any other DBMS but it is very difficult in operation activities like backup and restore, you have to develop some tools to achieve that. This approach is not recommended if you have big number of tenant.
参考资料：
1、multi-tenant database design： http://stackoverflow.com/questions/4769443/multi-tenant-database-design
2、How to design a multi tenant mysql database：http://stackoverflow.com/questions/5570102/how-to-design-a-multi-tenant-mysql-database
