What is SQL Schema and Why is it Used?
The SQL Schema is a blueprint (design) that shows how database objects are organized inside a database. These database objects include tables, views, and indexes.
If you create a table with columns, data types, and constraints, the schema keeps its basic structure. After that, the schema helps organize related database objects in a database.
Syntax:
CREATE SCHEMA schema_name;
Example:
Let you want to create a schema named StudentDB to organize student-related database objects.
CREATE SCHEMA StudentDB;
Output:
Query OK, 1 row affected
The StudentDB schema is created successfully. You can use it in SQL, which helps keep related objects organized.
How SQL Schema Works Internally?
An SQL Schema works internally through the following steps:
1. Write the CREATE SCHEMA Statement
First, you will write the CREATE SCHEMA statement with the schema name, and then you can execute it.
Example:
CREATE SCHEMA StudentDB;
2. Receive the Schema Name
When you run the schema statement, it goes to the SQL server, and the server receives the statement.
3. Check the Statement
The SQL server checks the statement which ensures that it is valid and the schema can be created.
4. Create the Schema
After checking the statement, if the SQL server finds it valid, then it creates the schema.
5. Record the Information
After creating the schema, the server saves information about it in the database system's metadata.
6. Ready to Use
When the schema information is recorded on the server, the schema is ready to use, which helps organize and manage related database objects.
What are Schema Objects and Why Are They Used?
The objects which are used in a database with tables for procedures, functions, and other database activities are called schema objects because they are also used inside a schema.
The list of schema objects is: tables, views, indexes, stored procedures, functions, and triggers.
They help store, manage, and access data in a database.
The Listing the Schema Objects with Their Works:
| Schema Object | Work |
|---|---|
| Tables | To store data in rows and columns. |
| Views | To show data from one or more tables. |
| Indexes | To find data quickly. |
| Stored Procedures | To save SQL statements for reuse. |
| Functions | are used to perform a task which returns a value. |
| Triggers | To automatically do an action when an event occurs. |
Advantages of SQL Schema
1. Organizes Database Objects
It keeps related database objects organized.
2. Improves Database Management
It makes database objects easy to manage.
3. Provides Logical Separation
It keeps different groups of database objects separate in the same database.
4. Helps Manage Access
It provides the to help in manage permission and control access to database objects.
5. Makes Database Structure Clear
It keeps the database structure clear and organized.
Common Mistakes When Using SQL Schema
If you use an SQL Schema, you should avoid these common mistakes:
Do Not Use an Incorrect Schema Name
You should check the schema name before creating or using a schema.
Do Not Create a Duplicate Schema Name
If you make a new schema, you should check whether the schema name already exists before creating it.
Do Not Use Objects in the Wrong Schema
Make sure tables and other database objects are created or accessed in the correct schema.
Do Not Ignore Access Permissions
Check the required permissions before working with schema objects.
Do Not Confuse a Schema with a Table
A schema organizes database objects, while a table stores data in rows and columns.
Difference Between Database and Schema
| Feature | Database | Schema |
|---|---|---|
| Meaning | It stores and manages data. | It is a blueprint (design) that organizes database objects. |
| Purpose | To store and manage data. | To organize related database objects. |
| Objects | It can keep schemas and their objects. | To keep objects that are tables, views, and indexes. |
| Structure | It gives the overall database structure. | It gives a logical structure for database objects. |
How to Alter a Schema?
To alter a schema, you should use the ALTER SCHEMA statement.
It is used to change the name of a schema or change its owner.
If you have to make changes to an existing schema, then you do not need to create a new schema.
You can rename the schema or assign its ownership to another existing user according to your needs.
Syntax to alter a schema:
ALTER SCHEMA schema_name [RENAME TO updated_schema_name] [OWNER TO updated_user_name]
Parameter:
schema_name: To keep the name of the existing schema which you want to change.
new_schema_name: To keep the new name which you want to give to the existing schema.
new_user_name: To keep the name of the existing user who will become the new owner of the schema.
Example:
If you have a schema named StudentDB and want to change its name to SchoolDB, use the following statement:
ALTER SCHEMA StudentDB RENAME TO SchoolDB;
Output:
The StudentDB schema is renamed to SchoolDB successfully.
In this example, to change the owner of the schema, you use the OWNER TO clause.The existing schema is StudentDB, and the new owner is AdminUser.
Example 2:
If you have a schema named StudentDB and want to change its owner to an existing user named AdminUser, use the following statement:
ALTER SCHEMA StudentDB OWNER TO AdminUser;
Output:
The owner of the StudentDB schema is changed to AdminUser successfully.
In this example, to change the owner of the schema, you use the OWNER TO clause.
The existing schema is StudentDB, and the new user is AdminUser.
The AdminUser must already exist as a user.
How to Rename a Schema?
To use the RENAME TO clause. It changes the schema name while keeping the same schema available.
For example, if you want to rename the StudentDB schema to SchoolDB, use:
ALTER SCHEMA StudentDB RENAME TO SchoolDB;
After using this statement, the schema name changes from StudentDB to SchoolDB.
How to change the Owner of a Schema?
To change the owner of a schema, use the OWNER TO clause in the statement, but remember that the new owner must already exist as a user.
For example, if you want to make AdminUser the owner of the StudentDB schema, use:
ALTER SCHEMA StudentDB OWNER TO AdminUser;
After using this statement, Admin User becomes the new owner of the Student DB schema.p>
