When deciding between SQL Server Express and PostgreSQL for .NET Core 2 web applications, it's essential to consider the unique advantages and disadvantages of each database in the context of the project's requirements.

Advantages of SQL Server Express:

1. Integration with .NET Core: SQL Server Express integrates seamlessly with .NET Core applications. It is optimized for Microsoft environments, and if you're already using other Microsoft products, this integration can simplify development and support.
2. Familiarity and Tools: SQL Server comes with powerful management tools like SQL Server Management Studio (SSMS), which makes database management, querying, and debugging easier. This can be a significant advantage for teams already familiar with Microsoft tools.
3. Scalability for Small to Medium Projects: SQL Server Express is free and provides a good option for small-to-medium-sized applications. It supports up to 10 GB of data per database, which is sufficient for many low-traffic applications.
4. Windows and Azure Compatibility: SQL Server Express is well-suited for Windows environments, and if your project is hosted on Azure, this option might be more advantageous because of the built-in compatibility and performance optimizations.

Disadvantages of SQL Server Express:

1. Limited Features: The Express edition has limitations in terms of features, such as lacking SQL Server Agent for scheduling jobs and restricted capabilities for concurrent users and database size (up to 10GB).
2. Performance Constraints: While SQL Server Express is free, it does not come with the high-end performance features found in the full version of SQL Server. This can become a bottleneck as your application grows, especially when it comes to advanced features like data compression or partitioning.
3. Platform Limitation: SQL Server Express is predominantly optimized for Windows, though it has limited Linux support. If your web application is designed for a cross-platform environment, PostgreSQL might offer better flexibility.

Advantages of PostgreSQL:

1. Cross-Platform Support: PostgreSQL works across multiple platforms, including Linux, macOS, and Windows. This makes it a great choice for cross-platform .NET Core applications.
2. Advanced Features: PostgreSQL supports advanced features like full-text search, JSONB support for storing JSON data efficiently, and custom data types. These features can provide flexibility when developing more complex or data-driven applications.
3. Performance and Concurrency: PostgreSQL has better concurrency management and scalability, especially for high-traffic applications. It performs well under heavy read/write loads and supports advanced indexing strategies.
4. Cost-Free and Open Source: Like SQL Server Express, PostgreSQL is free and open-source, but unlike SQL Server Express, it doesn’t have any significant limitations in terms of database size or features. It’s a great option for growing applications that may outgrow the limitations of SQL Server Express.

Disadvantages of PostgreSQL:

1. Learning Curve: PostgreSQL's advanced features can be complex for developers who are new to relational databases. Some features may require a deeper understanding of the database's internals.
2. Fewer Built-in Management Tools: Although PostgreSQL has management tools like pgAdmin, they are not as feature-rich as SQL Server Management Studio, which can be a disadvantage for teams that prefer a more comprehensive GUI-based management experience.
3. Ecosystem and Microsoft Support: While PostgreSQL is supported by .NET Core through the Npgsql library, it doesn't have the same deep integration with the Microsoft ecosystem as SQL Server. This might be a concern if your team is heavily invested in Microsoft tools.

Conclusion:

The choice between SQL Server Express and PostgreSQL depends largely on your project's specific requirements. If you're building a .NET Core 2 application that needs tight integration with Microsoft tools and services, SQL Server Express is a great choice, especially for small to medium-sized projects. On the other hand, if you're looking for a more flexible, cross-platform solution with advanced features and performance, PostgreSQL might be the better choice.

Both databases are solid options for .NET Core 2 applications, so your decision should be guided by factors such as scalability needs, platform requirements, and the team’s familiarity with the database systems. Must Read.