INSERT, UPDATE, DELETE ✏️

Add, Modify, and Remove Data - Zero to Hero

Beginner Friendly 45 min read Lesson 6 of 13

Master INSERT, UPDATE, DELETE in 2 Steps! 🎯

PART 1: Learn INSERT, UPDATE, DELETE in SSMS (SQL Server Management Studio)
PART 2: Use INSERT, UPDATE, DELETE in C# (Visual Studio)

Why These Commands Matter:

✅ INSERT - Add new data to your database
✅ UPDATE - Modify existing data
✅ DELETE - Remove data you no longer need
✅ Together they form CRUD (Create, Read, Update, Delete)

PART 1 - SQL Server Management Studio (SSMS)

Learn INSERT, UPDATE, DELETE in SSMS First!

SSMS Step 1: Create Our Sample Database

Let's create a simple Products table to practice with.

-- ===== CREATE DATABASE =====
CREATE DATABASE StoreDB;
GO

USE StoreDB;
GO

-- ===== CREATE PRODUCTS TABLE =====
CREATE TABLE Products (
    ProductId INT IDENTITY(1,1) PRIMARY KEY,
    Name NVARCHAR(100) NOT NULL,
    Price DECIMAL(10,2) NOT NULL,
    Quantity INT NOT NULL,
    Category NVARCHAR(50)
);
GO

-- ===== INSERT SAMPLE PRODUCTS =====
INSERT INTO Products (Name, Price, Quantity, Category)
VALUES 
    ('Laptop', 999.99, 10, 'Electronics'),
    ('Mouse', 25.50, 50, 'Electronics'),
    ('Keyboard', 45.00, 30, 'Electronics'),
    ('Monitor', 299.99, 15, 'Electronics'),
    ('Desk', 199.99, 5, 'Furniture'),
    ('Chair', 149.99, 8, 'Furniture');
GO

✅ Done! We have 6 products. Let's learn INSERT, UPDATE, DELETE!

😂 Fun Joke: Why did the developer create a Products table? Because they wanted to keep track of their "stock" options! 😅

SSMS Step 2: INSERT - Adding New Data

INSERT: This is how you add new records to your database. Like adding a new product to your store!

💻 INSERT - Add One Product

Add a single new product:

-- Insert one product
INSERT INTO Products (Name, Price, Quantity, Category)
VALUES 
    ('Headphones', 89.99, 20, 'Electronics');

✅ New product added!

📌 Important: Don't include ProductId - it auto-increments!

💻 INSERT - Add Multiple Products

Add multiple products at once:

-- Insert multiple products
INSERT INTO Products (Name, Price, Quantity, Category)
VALUES 
    ('Webcam', 59.99, 15, 'Electronics'),
    ('Desk Lamp', 35.00, 25, 'Furniture'),
    ('Coffee Mug', 12.99, 100, 'Kitchen');

✅ 3 new products added at once!

💻 INSERT - With SELECT (Copy Data)

Copy data from another table:

-- Insert from another table
INSERT INTO Products (Name, Price, Quantity, Category)
SELECT ProductName, Price, Stock, 'New'
FROM TempProducts
WHERE Price > 50;

✅ Copies only expensive products to the main table!

😂 Fun Joke: Why did the INSERT command go to the party? Because it wanted to add some new records! 😅

SSMS Step 3: UPDATE - Modifying Existing Data

UPDATE: This is how you change existing data. Like updating a product's price!

💻 UPDATE - Change Price

Update a specific product's price:

-- Update price of Laptop
UPDATE Products
SET Price = 899.99
WHERE Name = 'Laptop';

✅ Laptop price updated!

⚠️ Always use WHERE! Without it, ALL prices change!

💻 UPDATE - Multiple Columns

Update multiple fields at once:

-- Update both price and quantity
UPDATE Products
SET 
    Price = 27.99,
    Quantity = 60
WHERE Name = 'Mouse';

✅ Both price and quantity updated!

💻 UPDATE - With Calculations

Update using calculations:

-- Increase all prices by 10%
UPDATE Products
SET Price = Price * 1.10
WHERE Category = 'Electronics';

✅ All electronics prices increased by 10%!

💻 UPDATE - With WHERE Conditions

Update with multiple conditions:

-- Update products with low stock
UPDATE Products
SET Quantity = 20
WHERE Quantity < 10
AND Category = 'Electronics';

✅ Low-stock electronics restocked!

⚠️ WARNING! Always run SELECT first to see what you'll update!
SELECT * FROM Products WHERE Name = 'Laptop';
Then run UPDATE with the same WHERE clause!

SSMS Step 4: DELETE - Removing Data

DELETE: This is how you remove data from your database. Like removing a discontinued product!

💻 DELETE - Remove One Product

Delete a specific product:

-- Delete a specific product
DELETE FROM Products
WHERE Name = 'Desk Lamp';

✅ Desk Lamp removed!

⚠️ Always use WHERE! Without it, ALL rows are deleted!

💻 DELETE - With Conditions

Delete products with specific criteria:

-- Delete products with no stock
DELETE FROM Products
WHERE Quantity = 0
AND Category = 'Electronics';

✅ All out-of-stock electronics removed!

💻 Safe Practice - SELECT First!

Always test with SELECT before DELETE:

-- 1️⃣ First, see what will be deleted
SELECT * FROM Products
WHERE Category = 'Furniture'
AND Quantity < 5;

-- 2️⃣ If correct, run DELETE
DELETE FROM Products
WHERE Category = 'Furniture'
AND Quantity < 5;

✅ Safe! You know exactly what will be deleted!

⚠️ WARNING! DELETE is PERMANENT! There's no "undo" button!
Always SELECT first, then DELETE!

😂 Fun Joke: Why did the DELETE command break up with the table? Because it couldn't commit! (Get it? Commit? ...I'll stop 😅)

PART 2 - Using INSERT, UPDATE, DELETE in C#

Now Let's Use These Commands in C#!

C# Step 1: Create Your WinForms Project

Same commands, now in C#!

📁 Create Project

Open Visual Studio
Create Windows Forms App
Name it "ProductManager"

💻 Add NuGet Package

Install Microsoft.Data.SqlClient
Add using statements
Add connection string

using System.Data;
using Microsoft.Data.SqlClient;

private string connString = 
    "Server=localhost;Database=StoreDB;Trusted_Connection=True;TrustServerCertificate=True;";

C# Step 2: INSERT in C#

// ===== INSERT - Add a New Product =====

private void btnAdd_Click(object sender, EventArgs e)
{
    // 1️⃣ Get user input
    string name = txtName.Text;
    decimal price = decimal.Parse(txtPrice.Text);
    int quantity = int.Parse(txtQuantity.Text);
    string category = txtCategory.Text;
    
    // 2️⃣ The INSERT query
    string query = "INSERT INTO Products (Name, Price, Quantity, Category) " +
                  "VALUES (@Name, @Price, @Quantity, @Category)";
    
    // 3️⃣ Run the query
    using (var conn = new SqlConnection(connString))
    using (var cmd = new SqlCommand(query, conn))
    {
        cmd.Parameters.AddWithValue("@Name", name);
        cmd.Parameters.AddWithValue("@Price", price);
        cmd.Parameters.AddWithValue("@Quantity", quantity);
        cmd.Parameters.AddWithValue("@Category", category);
        
        conn.Open();
        int rows = cmd.ExecuteNonQuery();
        conn.Close();
        
        MessageBox.Show($"✅ {rows} product added!");
        LoadProducts();  // Refresh the list
    }
}

✅ Same as SSMS! The SQL is identical, just using parameters.

C# Step 3: UPDATE in C#

// ===== UPDATE - Modify a Product =====

private void btnUpdate_Click(object sender, EventArgs e)
{
    // 1️⃣ Get the product ID and new values
    int id = (int)dgvProducts.CurrentRow.Cells["ProductId"].Value;
    string name = txtName.Text;
    decimal price = decimal.Parse(txtPrice.Text);
    int quantity = int.Parse(txtQuantity.Text);
    string category = txtCategory.Text;
    
    // 2️⃣ The UPDATE query
    string query = "UPDATE Products SET Name=@Name, Price=@Price, " +
                  "Quantity=@Quantity, Category=@Category WHERE ProductId=@Id";
    
    // 3️⃣ Run the query
    using (var conn = new SqlConnection(connString))
    using (var cmd = new SqlCommand(query, conn))
    {
        cmd.Parameters.AddWithValue("@Name", name);
        cmd.Parameters.AddWithValue("@Price", price);
        cmd.Parameters.AddWithValue("@Quantity", quantity);
        cmd.Parameters.AddWithValue("@Category", category);
        cmd.Parameters.AddWithValue("@Id", id);
        
        conn.Open();
        int rows = cmd.ExecuteNonQuery();
        conn.Close();
        
        MessageBox.Show($"✅ {rows} product updated!");
        LoadProducts();  // Refresh the list
    }
}

✅ Same as SSMS! UPDATE with WHERE to target the right product.

C# Step 4: DELETE in C#

// ===== DELETE - Remove a Product =====

private void btnDelete_Click(object sender, EventArgs e)
{
    // 1️⃣ Confirm with user
    DialogResult result = MessageBox.Show(
        "Delete this product?",
        "Confirm Delete",
        MessageBoxButtons.YesNo,
        MessageBoxIcon.Warning);
    
    if (result != DialogResult.Yes) return;
    
    // 2️⃣ Get the product ID
    int id = (int)dgvProducts.CurrentRow.Cells["ProductId"].Value;
    
    // 3️⃣ The DELETE query
    string query = "DELETE FROM Products WHERE ProductId = @Id";
    
    // 4️⃣ Run the query
    using (var conn = new SqlConnection(connString))
    using (var cmd = new SqlCommand(query, conn))
    {
        cmd.Parameters.AddWithValue("@Id", id);
        
        conn.Open();
        int rows = cmd.ExecuteNonQuery();
        conn.Close();
        
        MessageBox.Show($"✅ {rows} product deleted!");
        LoadProducts();  // Refresh the list
    }
}

✅ Same as SSMS! DELETE with WHERE and user confirmation.

C# Step 5: Complete CRUD Application

CRUD = Create (INSERT), Read (SELECT), Update (UPDATE), Delete (DELETE)

// ===== COMPLETE PRODUCT MANAGEMENT SYSTEM =====

public partial class ProductForm : Form
{
    private string connString = "Server=localhost;Database=StoreDB;Trusted_Connection=True;TrustServerCertificate=True;";
    
    public ProductForm()
    {
        InitializeComponent();
        LoadProducts();
        ClearFields();
    }
    
    // ===== READ - Load All Products =====
    private void LoadProducts()
    {
        string query = "SELECT ProductId, Name, Price, Quantity, Category FROM Products";
        using (var conn = new SqlConnection(connString))
        using (var adapter = new SqlDataAdapter(query, conn))
        {
            DataTable dt = new DataTable();
            adapter.Fill(dt);
            dgvProducts.DataSource = dt;
            lblStatus.Text = $"📊 {dt.Rows.Count} products loaded";
        }
    }
    
    // ===== CREATE - INSERT =====
    private void btnAdd_Click(object sender, EventArgs e)
    {
        if (!ValidateFields()) return;
        
        string query = "INSERT INTO Products (Name, Price, Quantity, Category) " +
                      "VALUES (@Name, @Price, @Quantity, @Category)";
        
        using (var conn = new SqlConnection(connString))
        using (var cmd = new SqlCommand(query, conn))
        {
            AddParameters(cmd);
            conn.Open();
            int rows = cmd.ExecuteNonQuery();
            conn.Close();
            
            MessageBox.Show($"✅ Added {rows} product!");
            LoadProducts();
            ClearFields();
        }
    }
    
    // ===== UPDATE - UPDATE =====
    private void btnUpdate_Click(object sender, EventArgs e)
    {
        if (!ValidateFields()) return;
        
        int id = (int)dgvProducts.CurrentRow.Cells["ProductId"].Value;
        string query = "UPDATE Products SET Name=@Name, Price=@Price, " +
                      "Quantity=@Quantity, Category=@Category WHERE ProductId=@Id";
        
        using (var conn = new SqlConnection(connString))
        using (var cmd = new SqlCommand(query, conn))
        {
            AddParameters(cmd);
            cmd.Parameters.AddWithValue("@Id", id);
            conn.Open();
            int rows = cmd.ExecuteNonQuery();
            conn.Close();
            
            MessageBox.Show($"✅ Updated {rows} product!");
            LoadProducts();
            ClearFields();
        }
    }
    
    // ===== DELETE - DELETE =====
    private void btnDelete_Click(object sender, EventArgs e)
    {
        if (dgvProducts.CurrentRow == null) return;
        
        DialogResult result = MessageBox.Show(
            "Delete this product?", "Confirm",
            MessageBoxButtons.YesNo, MessageBoxIcon.Warning);
        
        if (result == DialogResult.No) return;
        
        int id = (int)dgvProducts.CurrentRow.Cells["ProductId"].Value;
        string query = "DELETE FROM Products WHERE ProductId = @Id";
        
        using (var conn = new SqlConnection(connString))
        using (var cmd = new SqlCommand(query, conn))
        {
            cmd.Parameters.AddWithValue("@Id", id);
            conn.Open();
            int rows = cmd.ExecuteNonQuery();
            conn.Close();
            
            MessageBox.Show($"✅ Deleted {rows} product!");
            LoadProducts();
            ClearFields();
        }
    }
    
    // ===== HELPERS =====
    private void AddParameters(SqlCommand cmd)
    {
        cmd.Parameters.AddWithValue("@Name", txtName.Text);
        cmd.Parameters.AddWithValue("@Price", decimal.Parse(txtPrice.Text));
        cmd.Parameters.AddWithValue("@Quantity", int.Parse(txtQuantity.Text));
        cmd.Parameters.AddWithValue("@Category", txtCategory.Text);
    }
    
    private bool ValidateFields()
    {
        if (string.IsNullOrWhiteSpace(txtName.Text))
        {
            MessageBox.Show("Please enter a name!");
            return false;
        }
        
        if (!decimal.TryParse(txtPrice.Text, out decimal _))
        {
            MessageBox.Show("Please enter a valid price!");
            return false;
        }
        
        if (!int.TryParse(txtQuantity.Text, out int _))
        {
            MessageBox.Show("Please enter a valid quantity!");
            return false;
        }
        
        return true;
    }
    
    private void ClearFields()
    {
        txtName.Clear();
        txtPrice.Clear();
        txtQuantity.Clear();
        txtCategory.Clear();
    }
    
    // ===== SELECT ROW =====
    private void dgvProducts_SelectionChanged(object sender, EventArgs e)
    {
        if (dgvProducts.CurrentRow == null) return;
        
        txtName.Text = dgvProducts.CurrentRow.Cells["Name"].Value?.ToString();
        txtPrice.Text = dgvProducts.CurrentRow.Cells["Price"].Value?.ToString();
        txtQuantity.Text = dgvProducts.CurrentRow.Cells["Quantity"].Value?.ToString();
        txtCategory.Text = dgvProducts.CurrentRow.Cells["Category"].Value?.ToString();
    }
}

🏆 Complete CRUD Application! You've built a full product management system!

Exercises: Test Your Skills!

1 Easy: INSERT a Product

Challenge: Write C# code to add a new product called "Tablet" with price 399.99, quantity 12, and category "Electronics".

// SOLUTION (3 lines)
string query = "INSERT INTO Products (Name, Price, Quantity, Category) VALUES (@Name, @Price, @Quantity, @Category)";
ExecuteQuery(query, new string[] { "@Name", "@Price", "@Quantity", "@Category" }, 
    new object[] { "Tablet", 399.99, 12, "Electronics" });
MessageBox.Show("Product added!");

2 Medium: UPDATE Products

Challenge: Write C# code to increase the price of all Electronics products by 15%.

// SOLUTION (3 lines)
string query = "UPDATE Products SET Price = Price * 1.15 WHERE Category = @Category";
ExecuteQuery(query, new string[] { "@Category" }, new object[] { "Electronics" });
MessageBox.Show("Prices updated!");

3 Hard: Complete Product Management

Challenge: Build a WinForms app with:

Add Product (INSERT)
Update Product (UPDATE)
Delete Product (DELETE)
Search by Category (SELECT + WHERE)
Sort by Price (ORDER BY)

// ===== COMPLETE SOLUTION =====

private void btnSearch_Click(object sender, EventArgs e)
{
    string query = "SELECT * FROM Products " +
                  "WHERE Category LIKE @Category " +
                  "ORDER BY Price " + (chkAsc.Checked ? "ASC" : "DESC");
    
    using (var conn = new SqlConnection(connString))
    using (var cmd = new SqlCommand(query, conn))
    {
        cmd.Parameters.AddWithValue("@Category", $"%{txtSearch.Text}%");
        using (var adapter = new SqlDataAdapter(cmd))
        {
            DataTable dt = new DataTable();
            adapter.Fill(dt);
            dgvProducts.DataSource = dt;
            lblStatus.Text = $"🔍 Found {dt.Rows.Count} products";
        }
    }
}

🏆 Congratulations! You've mastered INSERT, UPDATE, DELETE, and built a complete CRUD app!

🎉 Mastery Summary

INSERT

INSERT INTO Table VALUES (...)

Add new data

UPDATE

UPDATE Table SET Column = Value WHERE ...

Modify data

DELETE

DELETE FROM Table WHERE ...

Remove data

In SSMS

Write SQL directly

Learn the commands

In C#

ExecuteNonQuery()

Use in your apps

CRUD

Create, Read, Update, Delete

Complete application!

🎯 You're now a master of INSERT, UPDATE, and DELETE in SQL Server and C#!

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