⚙️ 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.

---

🛠 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).

---

🔹 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.

---

🔹 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.

---

🔹 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.

---

⚡ 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.

---

🧠 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.

---

🏁 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.

🧠 SQL vs T-SQL vs PostgreSQL — A Complete Guide for Developers

 🚀 Introduction

Databases are the heart of every modern application — whether you’re building a .NET Core Web API, a microservice, or a data analytics platform.
However, developers often get confused between SQL, T-SQL, and PostgreSQL — terms that sound similar but represent different layers of database technology.

In this article, you’ll clearly understand what each one means, where it fits, and how to use them effectively.

---

🧩 What is SQL?

SQL (Structured Query Language) is the standard language used to communicate with relational databases.
It defines how to store, retrieve, update, and delete data from tables.

💡 SQL Example

SELECT FirstName, LastName
FROM Employees
WHERE Department = 'HR';

🔍 Key Points:

• Developed by ANSI/ISO as a standard.

• Used by almost all relational databases (SQL Server, MySQL, PostgreSQL, Oracle, etc.).

• Syntax remains similar across systems, but behavior might differ slightly.

⚙️ Core SQL Operations

• DDL (Data Definition Language) → CREATE, ALTER, DROP

• DML (Data Manipulation Language) → SELECT, INSERT, UPDATE, DELETE

• DCL (Data Control Language) → GRANT, REVOKE

• TCL (Transaction Control Language) → COMMIT, ROLLBACK, SAVEPOINT

---

💼 What is T-SQL?

T-SQL (Transact-SQL) is Microsoft’s extension of SQL, used primarily with Microsoft SQL Server and Azure SQL Database.

It enhances standard SQL with programming features, such as:

• Variables

• Conditional logic (IF…ELSE)

• Loops

• Error handling (TRY...CATCH)

• Stored procedures and functions

💡 T-SQL Example

DECLARE @DeptName NVARCHAR(50) = 'HR';

SELECT EmployeeID, FirstName, LastName
FROM Employees
WHERE Department = @DeptName;

⚙️ T-SQL Features

Feature	Description
Variables	Declare and use variables inside queries
Control-of-flow	Use IF, WHILE, BEGIN...END blocks
Error handling	Built-in try-catch mechanisms
Stored procedures	Precompiled reusable SQL logic
Triggers	Automatically execute logic on table events

🧱 Use Case in .NET Core

When building a .NET Core Web API with SQL Server, your backend queries (through Entity Framework or ADO.NET) are translated into T-SQL commands executed by the database.

---

🌍 What is PostgreSQL?

PostgreSQL (also known as Postgres) is a powerful, open-source, object-relational database system (ORDBMS).
It follows the SQL standard but adds advanced features like JSON support, window functions, custom data types, and MVCC (Multi-Version Concurrency Control).

💡 PostgreSQL Example

SELECT name, salary
FROM employees
WHERE department = 'Finance'
ORDER BY salary DESC;

⚙️ Key Features of PostgreSQL

Feature	Description
Open Source	100% free and community-driven
Cross-Platform	Works on Linux, Windows, macOS
JSON Support	Perfect for semi-structured data
Advanced Indexing	B-tree, GIN, GiST, and Hash indexes
MVCC	High concurrency with data consistency
Extensions	Add-ons like PostGIS, pgcrypto, etc.

---

⚔️ SQL vs T-SQL vs PostgreSQL — Comparison Table

Feature	SQL	T-SQL	PostgreSQL
Definition	Standard query language	Microsoft’s SQL extension	Open-source relational DB
Used By	Many DB systems	SQL Server, Azure SQL	PostgreSQL
Procedural Features	Basic	Advanced (IF, WHILE, TRY-CATCH)	PL/pgSQL (Procedural SQL)
Platform	Generic	Microsoft-only	Cross-platform
JSON Support	Limited	Partial	Excellent
ACID Compliance	Yes	Yes	Yes
Licensing	Standard	Proprietary	Open-source
Performance	Depends on implementation	Optimized for SQL Server	Highly scalable, efficient
Best For	General relational DB work	Enterprise apps (Microsoft stack)	Cloud-native, hybrid, open systems

---

🧠 Real-Time Example in .NET Core + Web API

Suppose you are building an e-commerce microservice in .NET Core:

• SQL Server (T-SQL) → Store orders, payments, and user info (transactional data).

• PostgreSQL → Manage product catalog, search indexes, or analytics data (complex queries, JSON flexibility).

• SQL (standard) → Common language your ORM (like EF Core) uses to communicate with both databases.

Example Workflow:

Angular UI → .NET Core Web API → EF Core ORM → SQL Server (T-SQL)
                                   ↳ PostgreSQL (via Npgsql provider)

This hybrid setup allows best-of-both-worlds performance:

• SQL Server for business transactions

• PostgreSQL for flexible and analytics-heavy workloads

---

💬 Interview Questions & Answers

Q1. What is the main difference between SQL and T-SQL?
👉 SQL is a standard language; T-SQL is Microsoft’s extension adding procedural programming features.

Q2. Can PostgreSQL execute T-SQL code?
👉 No. PostgreSQL uses its own procedural language called PL/pgSQL.

Q3. Which is better — SQL Server or PostgreSQL?
👉 Depends on the project. SQL Server suits enterprise apps with Microsoft stack; PostgreSQL is ideal for open-source, cloud-native, or cross-platform projects.

Q4. Can I use PostgreSQL in .NET Core?
👉 Yes. Install Npgsql.EntityFrameworkCore.PostgreSQL package to integrate it seamlessly with EF Core.

Q5. What are the advantages of PostgreSQL over SQL Server?

• Open-source (no license cost)

• Better JSON and geospatial support

• Rich indexing and extensibility

---

🧭 When to Use What?

Scenario	Best Choice
Enterprise app on Azure	T-SQL (SQL Server)
Open-source or hybrid system	PostgreSQL
Generic database communication	Standard SQL
High concurrency analytics	PostgreSQL
Transaction-heavy microservices	SQL Server

---

🏁 Conclusion

While SQL forms the universal foundation, T-SQL adds Microsoft’s enterprise-level power, and PostgreSQL pushes open-source flexibility and innovation.

For .NET Core + Web API + Microservices developers, understanding all three helps you:

• Build scalable hybrid systems

• Optimize data performance

• Adapt to both enterprise and cloud-native architectures

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

Mastering them ensures you can work confidently across SQL Server, Azure, and PostgreSQL environments.