⚙️ SQL vs T-SQL vs PostgreSQL — Practical Code Comparison & EF Core Integration

 

🧩 1. Side-by-Side Query Comparison

Operation	SQL (Standard)	T-SQL (SQL Server)	PostgreSQL
Select Data	sql SELECT * FROM Employees;	sql SELECT * FROM Employees;	sql SELECT * FROM Employees;
Insert Record	sql INSERT INTO Employees (Name, Dept) VALUES ('Ravi', 'IT');	sql INSERT INTO Employees (Name, Dept) VALUES ('Ravi', 'IT');	sql INSERT INTO Employees (Name, Dept) VALUES ('Ravi', 'IT');
Declare Variable	❌ Not supported	sql DECLARE @Dept NVARCHAR(20) = 'HR'; SELECT * FROM Employees WHERE Dept = @Dept;	sql DO $$ DECLARE dept TEXT := 'HR'; BEGIN SELECT * FROM Employees WHERE Dept = dept; END $$;
String Concatenation	```sql SELECT FirstName		' '
Current Date	sql SELECT CURRENT_DATE;	sql SELECT GETDATE();	sql SELECT NOW();
Top / Limit	sql SELECT * FROM Employees FETCH FIRST 5 ROWS ONLY;	sql SELECT TOP 5 * FROM Employees;	sql SELECT * FROM Employees LIMIT 5;
Stored Procedure	Limited / Varies by DB	sql CREATE PROCEDURE GetEmployees AS BEGIN SELECT * FROM Employees; END;	sql CREATE FUNCTION GetEmployees() RETURNS TABLE(...) AS $$ SELECT * FROM Employees; $$ LANGUAGE sql;

✅ Takeaway:

• T-SQL adds variables, flow control, and procedural logic.

• PostgreSQL has its own procedural language PL/pgSQL with advanced functions and JSON operations.

• Standard SQL works across all, but lacks procedural capabilities.

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🛠 2. Entity Framework Core Setup in .NET Core Web API

Now let’s see how to connect .NET Core Web API with each database using Entity Framework Core (EF Core).

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🔹 A. SQL Server (T-SQL)

🧩 Install NuGet Package

dotnet add package Microsoft.EntityFrameworkCore.SqlServer

⚙️ appsettings.json

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=localhost;Database=EmployeeDB;User Id=sa;Password=Your@123;"
  }
}

⚙️ Program.cs

builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

🧱 Example Entity

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Department { get; set; }
}

✅ SQL Server uses T-SQL syntax internally for all queries EF Core generates.

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🔹 B. PostgreSQL

🧩 Install NuGet Package

dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL

⚙️ appsettings.json

{
  "ConnectionStrings": {
    "PostgresConnection": "Host=localhost;Database=EmployeeDB;Username=postgres;Password=admin123"
  }
}

⚙️ Program.cs

builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseNpgsql(builder.Configuration.GetConnectionString("PostgresConnection")));

✅ PostgreSQL queries generated by EF Core use PostgreSQL syntax, including features like LIMIT, RETURNING, and ILIKE.

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🔹 C. Generic SQL (Database Independent Example)

If you’re writing SQL logic that can work on both SQL Server and PostgreSQL, use standard SQL commands in EF Core’s LINQ or raw SQL:

var employees = await _context.Employees
    .Where(e => e.Department == "Finance")
    .OrderByDescending(e => e.Id)
    .Take(5)
    .ToListAsync();

✅ EF Core translates this query automatically to T-SQL (if SQL Server) or PostgreSQL syntax — making your code database-independent.

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⚡ 3. Real-Time Example: Hybrid Database Microservice

In real-world microservices:

• OrderService (SQL Server / T-SQL) → Handles transactional operations

• AnalyticsService (PostgreSQL) → Stores analytical data, JSON reports, or logs

Example Architecture:

Angular UI
   ↓
API Gateway (Ocelot)
   ↓
OrderService (.NET Core → EF Core → SQL Server)
   ↓
AnalyticsService (.NET Core → EF Core → PostgreSQL)

This architecture ensures high scalability and polyglot persistence, allowing each microservice to choose the most efficient database engine.

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🧠 Interview Q&A (EF + DB Context)

Q1. How does EF Core handle different databases?
👉 EF Core uses different providers (SqlServer, Npgsql, MySql, etc.) that translate LINQ queries into DB-specific SQL.

Q2. Can I switch from SQL Server to PostgreSQL easily?
👉 Yes, if you write queries using LINQ and avoid DB-specific T-SQL code.

Q3. What’s the main difference between EF Core SQL Server and EF Core PostgreSQL providers?
👉 SQL Server uses TOP, GETDATE(), IDENTITY; PostgreSQL uses LIMIT, NOW(), and SERIAL.

Q4. Is PostgreSQL good for microservices?
👉 Absolutely. It supports JSON, schema evolution, and strong concurrency — ideal for microservices and cloud-native apps.

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🏁 Conclusion

Use Case	Database	Query Type	EF Core Provider
Enterprise apps on Azure	SQL Server	T-SQL	Microsoft.EntityFrameworkCore.SqlServer
Open-source, cloud-based systems	PostgreSQL	SQL / PLpgSQL	Npgsql.EntityFrameworkCore.PostgreSQL
Database-agnostic logic	Any RDBMS	Standard SQL	Generic EF Core LINQ

SQL = The language
T-SQL = Microsoft’s dialect
PostgreSQL = The database engine

Mastering all three gives you the flexibility to design robust, cloud-ready microservices that run anywhere — from Azure to AWS to on-premises.