C# SQL Update Statement Example – C# Sql Command – C# SQL Update Statement Example

Purpose: – Illustrates using C# Sql Command Update statement and checking the result.
Prerequistes:

1. Install C# (Express or Standard Edition)
2. Install SQL Server Express
3. Download Northwind Database
4. Attach Northwind Database to Databases in Sql Express

Notes:

• Console Application is used to simplify things, but Windows Forms or Web Forms could also be used
• You can build a library of syntax examples by using same project over and over and just commenting out what you do not want to execute in Program.cs

Instructions:

1. Use C# 2008 (Express or Standard) Edition
2. Create new project; select Console Application; name of Project could be CSharp_Syntax.
3. Right-click project name in solution explorer; add new folder; name of folder could be DatabaseADONET
4. Right-click folder; add class; class name could be clsSqlCommandUpdate.cs
5. Copy code into clsSqlCommandUpdate.cs
6. Copy code into Program.cs
7. Click green arrow to start with debugging

Step 1: Use View Plain to Cut-n-paste code into clsSqlCommandUpdate.cs

 C# | 
  |
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using System;
using System.Data;
using System.Data.SqlClient;
 
 
public class clsSqlCommandUpdate
{
    //Create Connection
    SqlConnection thisConnection = new SqlConnection("server=(local)\\SQLEXPRESS;" + "integrated security=sspi;database=Northwind");
 
 
 
 
    public void Main()
    {
 
        OpenConnection();
 
        //Insert Rows to make sure they exist
        Console.WriteLine("\n");
        Console.WriteLine("***Insert Rows to make sure they exist***");
        InsertRows();
 
        //Display Rows Before Update
        Console.WriteLine("\n");
        Console.WriteLine("***Display Rows Before Update***");
        SelectRows();
 
        //Update Rows
        Console.WriteLine("\n");
        Console.WriteLine("***Perform Update***");
        UpdateRows();
 
        //Display Rows after update
        Console.WriteLine("\n");
        Console.WriteLine("***Display Rows After Update***");
        SelectRows();
 
        //Clean up with delete of all inserted rows
        Console.WriteLine("\n");
        Console.WriteLine("***Clean Up By Deleting Inserted Rows***");
        DeleteRows();
 
        // Close Connection
        thisConnection.Close();
        Console.WriteLine("Connection Closed");
 
        Console.ReadLine();
    }
    void OpenConnection()
    {
        try
        {
            // Open Connection
            thisConnection.Open();
            Console.WriteLine("Connection Opened");
        }
        catch (SqlException ex)
        {
            // Display error
            Console.WriteLine("Error: " + ex.ToString());
        }
    }
    void SelectRows()
    {
 
        try
        {
            // Sql Select Query 
            string sql = "SELECT * FROM Employees";
            SqlCommand cmd = new SqlCommand(sql, thisConnection);
 
            SqlDataReader dr;
            dr = cmd.ExecuteReader();
            string strEmployeeID = "EmployeeID";
            string strFirstName = "FirstName";
            string strLastName = "LastName";
 
            Console.WriteLine("{0} | {1} | {2}", strEmployeeID.PadRight(10), strFirstName.PadRight(10), strLastName);
            Console.WriteLine("==========================================");
            while (dr.Read())
            {
                //reading from the datareader
                Console.WriteLine("{0} | {1} | {2}", 
                    dr["EmployeeID"].ToString().PadRight(10), 
                    dr["FirstName"].ToString().PadRight(10), 
                    dr["LastName"]);
            }
            dr.Close();
            Console.WriteLine("==========================================");
        }
 
        catch (SqlException ex)
        {
            // Display error
            Console.WriteLine("Error: " + ex.ToString());
        }
 
    }
 
    void InsertRows()
    {
 
 
        //Insert Rows to make sure row exists before updating
        //Create Command object
        SqlCommand nonqueryCommand = thisConnection.CreateCommand();
 
        try
        {
 
            // Create INSERT statement with named parameters
            nonqueryCommand.CommandText = "INSERT  INTO Employees (FirstName, LastName) VALUES (@FirstName, @LastName)";
 
            // Add Parameters to Command Parameters collection
            nonqueryCommand.Parameters.Add("@FirstName", SqlDbType.VarChar, 10);
            nonqueryCommand.Parameters.Add("@LastName", SqlDbType.VarChar, 20);
 
            // Prepare command for repeated execution
            nonqueryCommand.Prepare();
 
            // Data to be inserted
            string[] names = { "Wade", "David", "Charlie" };
            for (int i = 0; i < = 2; i++)
            {
                nonqueryCommand.Parameters["@FirstName"].Value = names[i];
                nonqueryCommand.Parameters["@LastName"].Value = names[i];
 
                Console.WriteLine("Executing {0}", nonqueryCommand.CommandText);
                Console.WriteLine("Number of rows affected : {0}", nonqueryCommand.ExecuteNonQuery());
            }
        }
        catch (SqlException ex)
        {
            // Display error
            Console.WriteLine("Error: " + ex.ToString());
        }
        finally
        {
 
 
        }
 
    }
 
    void UpdateRows()
    {
 
        try
        {
            // 1. Create Command
            // Sql Update Statement
            string updateSql = "UPDATE Employees " + "SET LastName = @LastName " + "WHERE FirstName = @FirstName";
            SqlCommand UpdateCmd = new SqlCommand(updateSql, thisConnection);
 
            // 2. Map Parameters
 
            UpdateCmd.Parameters.Add("@FirstName", SqlDbType.NVarChar, 10, "FirstName");
 
            UpdateCmd.Parameters.Add("@LastName", SqlDbType.NVarChar, 20, "LastName");
 
            UpdateCmd.Parameters["@FirstName"].Value = "Wade";
            UpdateCmd.Parameters["@LastName"].Value = "Harvey";
 
            UpdateCmd.ExecuteNonQuery();
        }
 
        catch (SqlException ex)
        {
            // Display error
            Console.WriteLine("Error: " + ex.ToString());
        }
 
    }
 
    void DeleteRows()
    {
 
        try
        {
            //Create Command objects
            SqlCommand scalarCommand = new SqlCommand("SELECT COUNT(*) FROM Employees", thisConnection);
 
            // Execute Scalar Query
            Console.WriteLine("Before Delete, Number of Employees = {0}", scalarCommand.ExecuteScalar());
 
 
            // Set up and execute DELETE Command
            //Create Command object
            SqlCommand nonqueryCommand = thisConnection.CreateCommand();
            nonqueryCommand.CommandText = "DELETE FROM Employees WHERE " + "Firstname='Wade'  or " + "Firstname='Charlie' AND Lastname='Charlie' or " + "Firstname='David' AND Lastname='David' ";
            Console.WriteLine("Executing {0}", nonqueryCommand.CommandText);
            Console.WriteLine("Number of rows affected : {0}", nonqueryCommand.ExecuteNonQuery());
 
            // Execute Scalar Query
            Console.WriteLine("After Delete, Number of Employee = {0}", scalarCommand.ExecuteScalar());
        }
 
        catch (SqlException ex)
        {
            // Display error
            Console.WriteLine("Error: " + ex.ToString());
        }
 
    }
 
}
 
 
 

 C# | 
  |
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace CSharp_Syntax
{
    class Program
    {
        static void Main(string[] args)
        {
            //DatabaseADONET
 
 
             clsSqlCommandUpdate mySqlCommandUpdate = new clsSqlCommandUpdate();
            mySqlCommandUpdate.Main();
 
        }
    }
}