What are the main differences between PostgreSQL and Microsoft SQL Server database management systems?

PostgreSQL and Microsoft SQL Server are two popular database management systems (DBMS), but they have several key differences:

• License and openness: PostgreSQL is a fully open-source and free DBMS with open source code. Microsoft SQL Server is a proprietary system from Microsoft with paid licenses, although there are free versions with limitations (Express).

• Platform support: PostgreSQL runs on many OS — Linux, Windows, macOS. MS SQL Server is traditionally oriented towards Windows, but recent versions support Linux.

• Extensibility and standards: PostgreSQL is known for its extensibility, supporting user-defined data types, functions, operators. It strictly follows SQL standards and often introduces new features.

• Tools and integration: MS SQL Server is tightly integrated with the Microsoft ecosystem (.NET, Azure), and has powerful management tools (SSMS), analytics, and BI.

• Performance and scalability: Both DBMSs scale well, but MS SQL Server is often chosen for enterprise solutions with high load and complex analytical tasks.

• Support and community: PostgreSQL has a large community and many free resources. MS SQL Server is supported by Microsoft with official technical support.

Example usage:

-- Creating a table in PostgreSQL
CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Creating a table in MS SQL Server
CREATE TABLE users (
    id INT IDENTITY(1,1) PRIMARY KEY,
    name NVARCHAR(100),
    created_at DATETIME DEFAULT GETDATE()
);