Transitioning from SQL Server to PostgreSQL: Understanding the Schema Differences

preamble

As more and more organizations turn to open source technologies, commercial database administrators and developers are increasingly faced with the need to migrate to PostgreSQL. While SQL Server and PostgreSQL share many of the basic concepts of a database management system (RDBMS), the differences in how they handle certain constructs can be confusing, most notably the concept of a schema.

In SQL Server, schemas provide a flexible way of organizing objects, and while there is some similarity to PostgreSQL's schema structure, there are some important differences between the two in the details of user, permission, and object management.

What is Schema?

Before we discuss the differences between SQL Server and PostgreSQL, let's briefly define "schema". In a database system, a schema is a collection of database objects (e.g., tables, views, indexes, stored procedures, etc.). The schema provides a logical namespace for these objects, ensuring that each object is unique within that namespace. Although both SQL Server and PostgreSQL use schemas to organize database objects, there are some significant differences in their relationship and the role of schemas in practical administration.

A Schema Approach to SQL Server: Flexibility and Loose Coupling with Users

Patterns as Namespaces

In SQL Server, schemas provide a way to organize objects together and independently of user accounts. Each schema can be accessed by more than one user, unlike some other RDBMSs that are tightly coupled to a one-to-one correspondence with the user, such as Oracle. schemas in SQL Server are not only a logical grouping, but in this way they also provide more flexible rights management for the database.

For example, the default dbo (Database Owner) schema in SQL Server is a common namespace in which almost all users can create objects. In addition, SQL Server allows database administrators to create different schemas for different functions or departments, such as or, so that objects are logically separated in the same database for easy management and privilege assignment.

Fully qualified name of the object

In SQL Server, the fully qualified name of a table or view usually uses the schema_name.object_name format, for example. This naming scheme allows database administrators to organize database objects by function or business unit without strictly binding each schema to a user, which means that the schema does not have a one-to-one relationship with the user, and alternatively, you can ignore writing no schema and just write the object name object_name.

A Schema Approach to PostgreSQL: A Flexible Namespace Model

Patterns as Namespaces

Similar to SQL Server, schemas in PostgreSQL are namespaces, but are completely decoupled from user accounts.Schemas in PostgreSQL can contain multiple user-created objects, and objects in multiple schemas can be owned or accessed by the same user. It provides a modular structure for databases, allowing organizations to assign schemas based on function, department, or project.

As an example, if a schema is created in PostgreSQL for the HR department, the fully qualified name of the table will reflect the relationship between the schema and the object, theSimilar to the schema_name.object_name structure in SQL Server. However, PostgreSQL allows for more granular privilege management, where users can be granted privileges to specific schemas or objects based on business needs.

Decoupling Users and Models

In PostgreSQL, there is no mandatory binding between users and schemas. A user can own objects across multiple schemas, and multiple users can share the same schema. This flexibility greatly enhances PostgreSQL's ability to adapt to multi-user, multi-department collaboration.

PostgreSQL allows database administrators to simplify object access by setting up search paths, avoiding the need to always specify schema names in queries, and, like SQL Server, eliminating the need to overly rely on bindings between users and schemas.

Key Differences between SQL Server and PostgreSQL Schemas

Relationship between the model and the user

SQL Server: Schemas in SQL Server are user-independent and users can own or access objects across multiple schemas. Schemas are namespaces that are primarily used for logical organization and permission control.

PostgreSQL: PostgreSQL also decouples the schema from the user, and multiple users can own objects in the same schema. It is more flexible than SQL Server, allowing for a more modular database design.

Model creation and management

SQL Server: In SQL Server, schemas are usually generated automatically at database creation time (e.g., dbo), and administrators can explicitly create new schemas and assign them to different objects.

PostgreSQL: In PostgreSQL, schemas can be accessed via theCREATE SCHEMAcommand creates and allows multiple schemas to be created in a single database as needed, providing flexibility for grouping objects.

How the object is organized

SQL Server: In SQL Server, schemas are used to organize related objects (e.g., tables, views, stored procedures, etc.), which makes it easier to manage permissions and logical groupings. Schemas can be custom named according to business requirements.

PostgreSQL: Schemas in PostgreSQL are also used to organize database objects into logical groupings.

access control

SQL Server: Access control in SQL Server is implemented through roles and schemas. Users can be granted access to specific schemas or database objects.

PostgreSQL: PostgreSQL access control is also flexible and supports privilege management at both the schema level and the object level. Users can have access to objects across schemas through roles.

practical operation

Utilizing the search path

PostgreSQL's search path feature allows to simplify queries and avoid specifying schema names repeatedly. By properly configuring the search path, you can increase productivity.

Privilege management using roles

PostgreSQL's role system provides great flexibility for managing privileges across multiple schemas. You can create different roles based on your business needs and assign appropriate access rights to these roles.

summarize

The transition from SQL Server to PostgreSQL is basically not much different. In schema is used for logical grouping in both SQL Server and PostgreSQL.

PostgreSQL, like SQL Server, has schema flexibility and decoupled user relationships, making database management and organization more modular.

reference article

/docs/current/
/en-us/sql/relational-databases/security/authentication-access/create-a-database-schema?view=sql-server-ver16
/a-walkthrough-of-sql-schema/
/sqlserver/database-schema
/docs/current/
/en/what-is-a-schema-in-postgresql/

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