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.

# Types of database schema

There are two types of database schemas.

**Logical database schema:** This is best described as a design blueprint of how the data is organized and used by humans (not machines) to meet business requirements.

**Physical database schema:**
This represents how data is actually stored physically on disk storage. 

The difference between these two schemas is summarized in the table below.
  



# Types of keys

**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 code 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))

What is a database schema?

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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.
Types of database schema
There are two types of database schemas.
Logical database schema: This is best described as a design blueprint of how the data is organized and used by humans (not machines) to meet business requirements.
Physical database schema:
This represents how data is actually stored physically on disk storage.
The difference between these two schemas is summarized in the table below.
