Selecting from one Table and saving to another Table in the same database

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Web.Security;
using System.Security.Cryptography;

public partial class SubmitPage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
            SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["PasswordConnectionString"].ConnectionString);
            con.Open();


            string cmdStr = "Select INST_ID, EmailAddress from TableSecurity where EmailAddress='" + TextBoxEA.Text + "'";
            string cmdStr2 = "Select INST_ID, EmailAddress from TableCEO where EmailAddress ='" + TextBoxEA.Text + "'";
            string cmdStr3 = "Select INST_ID, EmailAddress from TableIALO where EmailAddress ='" + TextBoxEA.Text + "'";
            
            SqlCommand userExist = new SqlCommand(cmdStr, con);
            SqlCommand cmd = new SqlCommand("select INST_ID, EmailAddress from TableSecurity", con);
            SqlCommand cmd2 = new SqlCommand("select INST_ID, EmailAddress from TableCEO", con);
            SqlCommand cmd3 = new SqlCommand("select INST_ID, EmailAddress from TableIALO", con);
            int temp = Convert.ToInt32(userExist.ExecuteScalar().ToString());
            if (temp == 0)

                lblMessage.Text = "User Name Already Exist!!!<br /> Please Choose Another User Name.";
        }



    }

    protected void Submit_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["PasswordConnectionString"].ConnectionString);
        con.Open();

        string chkUser = "select INST_ID, EmailAddress from TableCEO where EmailAddress'" + TextBoxEA.Text + "";
        chkUser = "select INST_ID, EmailAddress from TableIALO where EmailAddress'" + TextBoxPW.Text + "";
        SqlCommand chkUsercmd = new SqlCommand(chkUser, con);

        
        string insCmd = "Insert into TableSecurity (INST_ID, EmailAddress, Password) values (@INST_ID, @EmailAddress, @Password)";
        SqlCommand insertUser = new SqlCommand(insCmd, con);
        insertUser.Parameters.AddWithValue("@EmailAddress", TextBoxEA.Text);
        insertUser.Parameters.AddWithValue("@Password", TextBoxPW.Text);
        insertUser.Parameters.AddWithValue("@INST_ID", TextBoxINST_ID.Text);
        


        try
        {
            insertUser.ExecuteNonQuery();
            con.Close();
            Response.Redirect("Login.aspx");
        }
        catch (Exception er)
        {
            Response.Write("An error occurred: " + er.Message);
        }
        finally
        {
        }
    }
    
}