Introduction to Schemas in SQL Server
Working with databases in SQL Server can be an exciting experience, especially if you are familiar with schemas. A schema is a logical container that holds multiple database objects such as tables, views, triggers, stored procedures, and indexes.
In simpler terms, a schema is like a folder in a file system that contains files of a similar type. When working with a database, schemas provide an organized and logical structure that helps to compartmentalize different objects within a database.
In this article, we will explore several aspects of schemas, including its definition, relationship with the database, naming conventions for objects within a schema, and much more.
Definition of a schema
A schema, in SQL Server, is a logical container that groups related database objects together. A schema exists within a database and is defined as a namespace for database objects.
This means that a schema determines the scope or visibility of database objects to other objects within the database. The schema helps to differentiate between objects that have the same name and provides a structure to organize different objects within a database.
Schema owner and association with username
In SQL Server, every schema must have a schema owner defined. The schema owner is a user or login that is responsible for creating and managing objects within the schema.
All objects within a schema, when created by the owner, have the name schema_name.object_name
(e.g., sales.customer). By default, the schema owner is the user who creates the schema, but it is possible to transfer the ownership of the schema to another user.
The schema owner and username associated with it help to identify the user responsible for creating and managing the database objects.
Relationship between schema and database
In SQL Server, a database can have multiple schemas, and each schema is a logical container of related database objects. A schema, therefore, provides an organizational structure within a database and helps to isolate and compartmentalize objects within a database.
Multiple schemas can exist within a database, and each schema can have its own set of objects, security settings, and a unique schema owner. When creating a new database, the default schema for the user can be specified, which will be used as the default for all objects.
Naming conventions for objects within a schema
SQL Server has several rules for naming conventions for objects within a schema. Each object must have a unique name within its schema, and the same name can be reused in a different schema.
The name of an object in the schema must follow the format schema_name.object_name. Object names are not case sensitive, but it is recommended to follow a consistent naming convention to maintain consistency and improve readability.
Some organizations have established naming conventions that they require to be followed explicitly, and it is advisable to adopt such conventions when developing applications for those organizations.
Built-in Schemas in SQL Server
SQL Server has several pre-defined schemas that are reserved for specific purposes and cannot be renamed or deleted. These schemas can be categorized into four types: user-defined schemas, system schemas, pre-defined schemas, and temporal table schemas.
The pre-defined schemas available in SQL Server include the following:
1) dbo schema – The dbo schema is the default schema and is created automatically when a new database is created. It is the primary schema used to store user-defined objects within the database.
2) guest schema – The Guest schema is a special schema used to regulate access to the database when the user is not explicitly assigned a user account. This schema does not have a schema owner and has limited permissions, making it less secure for user-defined objects.
3) sys schema – The sys schema contains system tables and views that store metadata information about the database. This schema is used for internal purposes only, and its objects cannot be renamed or deleted.
4) INFORMATION_SCHEMA schema – The INFORMATION_SCHEMA schema is a system schema used to provide user-read access to metadata information about the database. This schema contains database object definitions, user-defined data types, and column-level information.
Reservation of sys and INFORMATION_SCHEMA schemas for system objects
SQL Server reserves the sys and INFORMATION_SCHEMA schemas for system objects such as system tables, views, and stored procedures. These schemas are reserved, and their objects cannot be renamed and are not visible to users unless they are explicitly granted permission.
They are also not included in the default schema search path when resolving object references, which means that explicit references to those objects must be used or implicitly included in the references.
Default schema for a newly created database
The dbo schema is the default schema for a newly created database in SQL Server. However, you can specify a different default schema when creating a new user account using the CREATE USER command.
The command syntax for specifying a default schema is as follows:
CREATE USER [username] WITH DEFAULT_SCHEMA = [schema_name];
Conclusion
Schemas are an essential component of database design in SQL Server. They provide an organized and logical structure for objects within a database, which helps to enhance readability and simplify management.
Understanding the relationship between schemas and databases, naming conventions, and pre-defined schemas helps to optimize a database environment. For those looking to scale their database projects, schemas are a viable option to explore and implement.
3) Creating a new Schema using CREATE SCHEMA statement
In SQL Server, creating a new schema can be done using the CREATE SCHEMA statement. The CREATE SCHEMA statement creates a schema in the current database and is used to group related database objects together.
The syntax of the CREATE SCHEMA statement is as follows:
CREATE SCHEMA schema_name
[AUTHORIZATION owner_name];
The parameters of the CREATE SCHEMA statement are as follows:
– schema_name: The name of the schema to be created. – AUTHORIZATION owner_name: The owner of the schema.
Specifying schema name and owner
When creating a new schema using the CREATE SCHEMA statement, you need to specify the schema name and the owner of the schema. The schema name is the name of the new schema you wish to create.
The owner is the name of the user account that will be associated with the schema. If you do not specify an owner, the current user executing the CREATE SCHEMA statement will be the default owner.
You can optionally specify the owner of the schema by using the AUTHORIZATION keyword followed by the owner’s name. For example, to create a new schema named customer_services owned by user account “johnsmith”, you would use the CREATE SCHEMA statement as follows:
CREATE SCHEMA customer_services AUTHORIZATION johnsmith;
Example of creating a new schema
Let’s say that you need to create a new schema for your organization’s HR department. You can use the following example of the CREATE SCHEMA statement to create the schema:
CREATE SCHEMA HR AUTHORIZATION jane_smith;
This statement creates a new schema named “HR” with Jane Smith as the owner of the schema.
Listing schemas in the current database using sys.schemas
Once you have created a schema in SQL Server, you can use the sys.schemas query to list all the schemas in the current database. The query to list all the schemas is as follows:
SELECT name
FROM sys.schemas;
To find the “HR” schema that we created in our example, you can add a WHERE clause to the query to filter by schema name as follows:
SELECT name
FROM sys.schemas
WHERE name = ‘HR’;
This query lists only the “HR” schema, making it easier to locate the schema that you have created.
4) Creating Objects within a Schema
After creating a schema, you can create different objects within it. These objects can include tables, views, triggers, stored procedures, or indexes.
To create an object within a schema, you need to specify the schema name and object name when creating the object.
Creating a new table in a schema
To create a new table within a schema, you can use the CREATE TABLE statement with the schema name prefix as follows:
CREATE TABLE customer_services.jobs
(
job_id INT PRIMARY KEY,
job_title NVARCHAR
(50) NOT NULL,
min_salary INT NOT NULL,
max_salary INT NOT NULL
);
This statement creates a new table called “jobs” within the “customer_services” schema. The table has four columns named “job_id,” “job_title,” “min_salary,” and “max_salary.” The “job_id” column is declared as the primary key of the table.
Other objects that can be created in a schema
Apart from creating tables, you can also create other objects within a schema, such as views, triggers, stored procedures, and indexes. To create these objects within a schema, you need to specify the schema name prefix when creating the object.
To create a view in the “customer_services” schema, you can use the following syntax:
CREATE VIEW customer_services.view_name
AS
SELECT … To create a trigger in the “customer_services” schema, you can use the following syntax:
CREATE TRIGGER customer_services.trigger_name
ON table_name
FOR INSERT, UPDATE, DELETE
AS
… To create a stored procedure in the “customer_services” schema, you can use the following syntax:
CREATE PROCEDURE customer_services.procedure_name
AS
BEGIN
…
END
To create an index in the “customer_services” schema, you can use the following syntax:
CREATE INDEX customer_services.index_name
ON table_name
(column_name);
Conclusion
Schemas in SQL Server provide an organized and logical structure for database objects. Creating schemas can be done using the CREATE SCHEMA command with the syntax specifying the name and the owner.
When creating objects within a schema, the schema and object name must be specified, with the prefix of the schema name used. Different objects can be created, including tables, views, triggers, stored procedures, and indexes.
Maintenance of the schema data must be carefully managed to allow for effective query and indexing, avoiding errors that could result in application failure. In summary, schemas in SQL Server provide a structured and effective way to organize and manage database objects.
Schemas can contain multiple objects such as tables, views, triggers, stored procedures, and indexes, and provide a logical structure that simplifies navigation within a database. The ownership of these objects, as well as the naming conventions used, is specified using the CREATE SCHEMA command, which helps to maintain consistency across the database.
Creating objects within a schema can be done using the schema name prefix, while careful management of the schema data is necessary to avoid errors. Schemas are essential components of a SQL Server database, and mastering them is a crucial skill for developers working with databases.