In Microsoft SQL Server, schemas are a database object that serve as a logical container for organizing and managing database objects such as tables, views, procedures, and functions. Schemas provide a way to group related objects together and control access to them. Here are key details about schemas in SQL Server:

1. Logical Organization:

• Schemas provide a way to logically organize database objects. You can think of a schema as a container that holds related tables and other objects.

2. Ownership and Permissions:

• Each schema is typically associated with a database user, referred to as the schema owner. The owner has control over the objects within the schema.
• Permissions to access objects within a schema can be granted or denied to other users and roles, allowing for fine-grained access control.

3. Default Schema:

• When a user creates an object without specifying a schema name, SQL Server assigns it to the user’s default schema.
• You can set a user’s default schema using the ALTER USER statement.

4. Multiple Schemas:

• A single SQL Server database can contain multiple schemas, each with its own set of objects.
• This is particularly useful when you have different teams or applications sharing a database but needing separate namespaces for their objects.

5. Schema Naming:

• Schemas are typically named to reflect their purpose or the type of objects they contain.
• Common schema names include “dbo” (the default schema), “hr” for HR-related objects, “sales” for sales-related objects, and so on.

6. Schema Creation:

• You can create a new schema using the CREATE SCHEMA statement and specify the schema owner.

CREATE SCHEMA schema_name AUTHORIZATION owner_name;

7. Object Naming within Schemas:

• Objects within a schema are referenced using the schema name as a prefix.
• For example, if you have a schema named “sales” and a table named “orders” within that schema, you would reference it as “sales.orders” when querying.

8. Schema Usage:

• Schemas are commonly used to:
  • Group tables related to a specific application module or department.
  • Isolate and manage database objects created by different users or applications.
  • Simplify object management and organization in large databases.

9. Built-In Schemas:

• SQL Server includes several built-in schemas such as “dbo” (the default schema), “sys” (system schema), “guest” (for users who do not have a specific schema), and “INFORMATION_SCHEMA” (for metadata and catalog views).

10. Ownership Chaining:

• SQL Server uses ownership chaining to control access to objects within a schema. If a user has access to an object in a schema, they can access other objects in the same schema without explicit permissions, as long as the object references are within the same ownership chain.

Schemas provide a valuable way to organize and secure database objects in SQL Server. They help manage object ownership, control access, and improve the overall organization of database structures. When designing database schemas, it’s essential to consider the logical organization of objects and the access control requirements of your application.