Hi smile,

Check this example. Now please take its reference and correct your code.

For reading excel i have used ClosedXML. You can refer below link for more details.

Read and import Excel file data to DataGridView using ClosedXml using C# and VB.Net

I have added two Button controls, one DataGridView control and one OpenFileDialog control in the Form.

Namespaces

C#

using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using ClosedXML.Excel;

VB.Net

Imports System.ComponentModel
Imports System.Data
Imports System.Data.SqlClient
Imports System.Linq
Imports ClosedXML.Excel

Code

C#

public partial class Form1 : Form
{
    private static DataTable dt;

    public Form1()
    {
        InitializeComponent();
    }

    private void btnImport_Click(object sender, EventArgs e)
    {
        openFileDialog1.ShowDialog();
    }

    private void openFileDialog1_FileOk(object sender, CancelEventArgs e)
    {
        string filePath = openFileDialog1.FileName;

        using (XLWorkbook workBook = new XLWorkbook(filePath))
        {
            IXLWorksheet workSheet = workBook.Worksheet(1);

            dt = new DataTable();

            bool firstRow = true;
            foreach (IXLRow row in workSheet.Rows())
            {
                if (firstRow)
                {
                    foreach (IXLCell cell in row.Cells())
                    {
                        dt.Columns.Add(cell.Value.ToString());
                    }
                    firstRow = false;
                }
                else
                {
                    dt.Rows.Add();
                    int i = 0;
                    foreach (IXLCell cell in row.Cells())
                    {
                        dt.Rows[dt.Rows.Count - 1][i] = cell.Value.ToString();
                        i++;
                    }
                }

                dataGridView1.DataSource = dt;
                dataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill;
            }
        }
    }

    private void btnSave_Click(object sender, EventArgs e)
    {
        DataTable dtStudent = dt.Copy();

        DataTable dtClass = new DataTable();
        dtClass.Columns.Add("ClassID", typeof(int));
        dtClass.Columns.Add("ClassName", typeof(string));
        object[] classNames = dt.AsEnumerable().Select(x => x["ClassName"]).Distinct().ToArray();
        for (int i = 0; i < classNames.Length; i++)
        {
            DataRow dr = dtClass.NewRow();
            dr["ClassID"] = i + 1;
            dr["ClassName"] = classNames[i];
            dtClass.Rows.Add(dr);
            // Insert into tblClass.
            SqlCommand cmdClass = new SqlCommand();
            cmdClass.CommandText = "INSERT INTO tblClass (ClassID,ClassName) VALUES (@ClassID,@ClassName)";
            cmdClass.Parameters.AddWithValue("@ClassID", i + 1);
            cmdClass.Parameters.AddWithValue("@ClassName", classNames[i]);
            Insert(cmdClass);
        }

        DataTable dtSection = new DataTable();
        dtSection.Columns.Add("SectionID", typeof(int));
        dtSection.Columns.Add("ClassID", typeof(int));
        dtSection.Columns.Add("SectionName", typeof(string));
        var sections = dt.AsEnumerable()
            .Select(x => new
            {
                SectionName = x["SectionName"],
                ClassName = x["ClassName"]
            }).Distinct().ToList();


        for (int i = 0; i < sections.Count; i++)
        {
            DataRow dr = dtSection.NewRow();
            dr["SectionID"] = i + 1;
            dr["ClassID"] = dtClass.Select("ClassName='" + sections[i].ClassName + "'").FirstOrDefault().Field<int>("ClassID");
            dr["SectionName"] = sections[i].SectionName;
            dtSection.Rows.Add(dr);
            // Insert into tblSection.
            SqlCommand cmdSection = new SqlCommand();
            cmdSection.CommandText = "INSERT INTO tblSection (SectionID,ClassID,SectionName) VALUES (@SectionID,@ClassID,@SectionName)";
            cmdSection.Parameters.AddWithValue("@SectionID", i + 1);
            cmdSection.Parameters.AddWithValue("@ClassID", dtClass.Select("ClassName='" + sections[i].ClassName + "'").FirstOrDefault().Field<int>("ClassID"));
            cmdSection.Parameters.AddWithValue("@SectionName", sections[i].SectionName);
            Insert(cmdSection);
        }

        foreach (DataRow dr in dtStudent.Rows)
        {
            dr["ClassName"] = dtClass.AsEnumerable().Where(x => x["ClassName"] == dr["ClassName"]).Select(x => x["ClassID"]).FirstOrDefault();
            dr["SectionName"] = dtSection.AsEnumerable().Where(x => x["SectionName"] == dr["SectionName"]).Select(x => x["SectionID"]).FirstOrDefault();
            //Insert into tblStudent.
            SqlCommand cmdStudent = new SqlCommand();
            cmdStudent.CommandText = "INSERT INTO tblStudent (StuID,StuName,FName,ClassID,SectionID) VALUES (@StuID,@StuName,@FName,@ClassID,@SectionID)";
            cmdStudent.Parameters.AddWithValue("@StuID", dr["StuID"]);
            cmdStudent.Parameters.AddWithValue("@StuName", dr["StuName"]);
            cmdStudent.Parameters.AddWithValue("@FName", dr["FName"]);
            cmdStudent.Parameters.AddWithValue("@ClassID", dr["ClassName"]);
            cmdStudent.Parameters.AddWithValue("@SectionID", dr["SectionName"]);
            Insert(cmdStudent);
        }
    }

    private void Insert(SqlCommand cmd)
    {
        string conString = @"Server=.;DataBase=Test;UID=sa;PWD=pass@123";
        using (SqlConnection con = new SqlConnection(conString))
        {
            con.Open();
            cmd.Connection = con;
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }
}

VB.Net

Public Class Form1

    Private Shared dt As DataTable

    Public Sub New()
        InitializeComponent()
    End Sub

    Private Sub btnImport_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnImport.Click
        openFileDialog1.ShowDialog()
    End Sub

    Private Sub openFileDialog1_FileOk(sender As Object, e As CancelEventArgs) Handles openFileDialog1.FileOk
        Dim filePath As String = openFileDialog1.FileName
        Using workBook As XLWorkbook = New XLWorkbook(filePath)
            Dim workSheet As IXLWorksheet = workBook.Worksheet(1)
            dt = New DataTable()
            Dim firstRow As Boolean = True
            For Each row As IXLRow In workSheet.Rows()
                If firstRow Then
                    For Each cell As IXLCell In row.Cells()
                        dt.Columns.Add(cell.Value.ToString())
                    Next
                    firstRow = False
                Else
                    dt.Rows.Add()
                    Dim i As Integer = 0
                    For Each cell As IXLCell In row.Cells()
                        dt.Rows(dt.Rows.Count - 1)(i) = cell.Value.ToString()
                        i += 1
                    Next
                End If

                dataGridView1.DataSource = dt
                dataGridView1.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill
            Next
        End Using
    End Sub

    Private Sub btnSave_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnSave.Click
        Dim dtStudent As DataTable = dt.Copy()
        Dim dtClass As DataTable = New DataTable()
        dtClass.Columns.Add("ClassID", GetType(Integer))
        dtClass.Columns.Add("ClassName", GetType(String))
        Dim classNames As Object() = dt.AsEnumerable().[Select](Function(x) x("ClassName")).Distinct().ToArray()

        For i As Integer = 0 To classNames.Length - 1
            Dim dr As DataRow = dtClass.NewRow()
            dr("ClassID") = i + 1
            dr("ClassName") = classNames(i)
            dtClass.Rows.Add(dr)
            Dim cmdClass As SqlCommand = New SqlCommand()
            cmdClass.CommandText = "INSERT INTO tblClass (ClassID,ClassName) VALUES (@ClassID,@ClassName)"
            cmdClass.Parameters.AddWithValue("@ClassID", i + 1)
            cmdClass.Parameters.AddWithValue("@ClassName", classNames(i))
            Insert(cmdClass)
        Next

        Dim dtSection As DataTable = New DataTable()
        dtSection.Columns.Add("SectionID", GetType(Integer))
        dtSection.Columns.Add("ClassID", GetType(Integer))
        dtSection.Columns.Add("SectionName", GetType(String))
        Dim sections = dt.AsEnumerable().Select(Function(x) New With {Key _
                            .SectionName = x("SectionName"), Key _
                            .ClassName = x("ClassName")
                        }).Distinct().ToList()

        For i As Integer = 0 To sections.Count - 1
            Dim dr As DataRow = dtSection.NewRow()
            dr("SectionID") = i + 1
            dr("ClassID") = dtClass.[Select]("ClassName='" & sections(i).ClassName & "'").FirstOrDefault().Field(Of Integer)("ClassID")
            dr("SectionName") = sections(i).SectionName
            dtSection.Rows.Add(dr)
            Dim cmdSection As SqlCommand = New SqlCommand()
            cmdSection.CommandText = "INSERT INTO tblSection (SectionID,ClassID,SectionName) VALUES (@SectionID,@ClassID,@SectionName)"
            cmdSection.Parameters.AddWithValue("@SectionID", i + 1)
            cmdSection.Parameters.AddWithValue("@ClassID", dtClass.[Select]("ClassName='" & sections(i).ClassName & "'").FirstOrDefault().Field(Of Integer)("ClassID"))
            cmdSection.Parameters.AddWithValue("@SectionName", sections(i).SectionName)
            Insert(cmdSection)
        Next

        For Each dr As DataRow In dtStudent.Rows
            dr("ClassName") = dtClass.AsEnumerable().Where(Function(x) x("ClassName") = dr("ClassName")).[Select](Function(x) x("ClassID")).FirstOrDefault()
            dr("SectionName") = dtSection.AsEnumerable().Where(Function(x) x("SectionName") = dr("SectionName")).[Select](Function(x) x("SectionID")).FirstOrDefault()
            Dim cmdStudent As SqlCommand = New SqlCommand()
            cmdStudent.CommandText = "INSERT INTO tblStudent (StuID,StuName,FName,ClassID,SectionID) VALUES (@StuID,@StuName,@FName,@ClassID,@SectionID)"
            cmdStudent.Parameters.AddWithValue("@StuID", dr("StuID"))
            cmdStudent.Parameters.AddWithValue("@StuName", dr("StuName"))
            cmdStudent.Parameters.AddWithValue("@FName", dr("FName"))
            cmdStudent.Parameters.AddWithValue("@ClassID", dr("ClassName"))
            cmdStudent.Parameters.AddWithValue("@SectionID", dr("SectionName"))
            Insert(cmdStudent)
        Next
    End Sub

    Private Sub Insert(ByVal cmd As SqlCommand)
        Dim conString As String = "Server=.;DataBase=Test;UID=sa;PWD=pass@123"
        Using con As SqlConnection = New SqlConnection(conString)
            con.Open()
            cmd.Connection = con
            cmd.ExecuteNonQuery()
            con.Close()
        End Using
    End Sub
End Class

Screenshot

The form

Database record on save Button click