what is database this is an example of many to one (often written as many: relationshipthat is there are many people who can live at one address (in the above adam smith also lives at address 'addr 'in relational databases there can be several different types of relationship such asone:one where only one row in one table references one and only one row in another table an example of one to one relationship might be from person to an order for unique piece of jewellery one:many this is the same as the above address examplehowever in this case the direction of the relationship is reversed (that is to say that one address in the addresses table can reference multiple persons in the people tablemany:many this is where many rows in one table may reference many rows in second table for examplemany students may take particular class and student may take many classes this relationship usually involves an intermediate (jointable to hold the associations between the rows the database schema the structure of relational database is defined using data definition language or data description language ( ddltypicallythe syntax of such language is limited to the semantics (meaningrequired to define the structure of the tables this structure is known as the database schema typicallythe ddl has commands such as create tabledrop table (to delete tableand alter table (to modify the structure of an existing tablemany tools provided with database allow you to define the structure of the database without getting too bound up in the syntax of the ddlhoweverit is useful to be aware of it and to understand that the database can be created in this way for examplewe will use the mysql database in this the mysql