A database schema is an abstraction used to represent the storage of data in a database. It not only describes the organization of data but also represents the relationship between various tables in a database.
There are two types of database schemas.
This represents how the data is organized in terms of tables, and how the different attributes in the different tables link them. Different
database management systems use different syntax to define the logical architecture and constraints of a database which is called logical database schema.
This represents how data is stored physically on disk storage.
The difference between these two schemas could be seen in the table below.
Database schema is Just a representation and it does not contain any data.
Two important types of keys are:
Primary key: It is used to uniquely identify a record in the table.
Foreign key It is an attribute that is used as a primary key in another table.
The following cope snippet defines the schema of a table(mapdata) in MySQL.
CREATE TABLE mapdata ( id integer NOT NULL AUTO_INCREMENT, mapid integer NOT NULL, x integer NOT NULL, y integer NOT NULL, z integer NOT NULL, value varchar(1), UNIQUE KEY(id))
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