如何检查数据库中是否已存在值并显示验证消息

Question

I have the below code, that connects to a Sql database and insert's data into a table :

string firstNameV = txtFname.Text;
string surnameV = txtSname.Text;
string emailV = txtEmail.Text;

SqlConnection conn = new   SqlConnection(ConfigurationManager.ConnectionStrings["myConnectionString"].ToString());

SqlCommand cmd = new SqlCommand();

cmd.CommandText = "INSERT INTO EmailSignUp (Title,FirstName,Surname,Email,EstablishmentType,Interests) VALUES (@Title,@FirstName,@Surname,@Email,@EstablishmentType,@Interests)";

cmd.Parameters.Add("@Title", SqlDbType.NVarChar).Value = title;
cmd.Parameters.Add("@FirstName", SqlDbType.NVarChar).Value = firstNameV;
cmd.Parameters.Add("@Surname", SqlDbType.NVarChar).Value = surnameV;
cmd.Parameters.Add("@Email", SqlDbType.NVarChar).Value = emailV;
cmd.Parameters.Add("@EstablishmentType", SqlDbType.NVarChar).Value = eType;
cmd.Parameters.Add("@Interests", SqlDbType.NVarChar).Value = ins;

cmd.Connection = conn;

conn.Open();

cmd.ExecuteNonQuery();
conn.Close();

How do I check if an email being entered in the "txtEmail" text box already exists in my database, in the email column and then alert message saying email already exists so it doesn't get inserted into my database?

Answer 1

Call this method in required textbox or area

public void EmailCheck()
    {
        string constring = ConfigurationManager.ConnectionStrings["ConnData"].ConnectionString;
        SqlConnection con = new SqlConnection(constring);
        SqlCommand cmd = new SqlCommand("Select * from EmailSignUp where EmailId= @EmailId", con);
        cmd.Parameters.AddWithValue("@EmailId", this.txtEmail.Text);
        con.Open();
        SqlDataReader dr = cmd.ExecuteReader();
        while (dr.Read())
        {
            if (dr.HasRows == true)
            {
                MessageBox.Show("EmailId = " + dr[5].ToString() + " Already exist");
                txtEmail.Clear();
                break;
            }
        }

    }

Answer 2

Try this

cmd.CommandText = "IF NOT EXISTS(SELECT * FROM EmailSignUp WHERE Email = '" 
+ txtEmail.Text + "') 
BEGIN
INSERT INTO EmailSignUp (Title,FirstName,Surname,Email,EstablishmentType,Interests) VALUES (@Title,@FirstName,@Surname,@Email,@EstablishmentType,@Interests) 
END";

Answer 3

Call a stored Procedure and inside the stored procedure you can check before insert

 IF NOT EXISTS(SELECT * FROM EmailSignUp WHERE Email =@email)   
 Begin
insert query here
 end

In another way you can check it in text changed event also

Answer 4

Create a procedure on SQL server and check whether the name exists or not

    CREATE PROCEDURE Procedure_Name 
@mystring varchar(100),
@isExist bit out
AS
BEGIN
    if exists(select column1 from tblTable1 where column1=@mystring)
    begin
    select @isExist=1
    end
    else
    begin
    select @isExist=0
    end


END
GO

This is a sample procedure. If @isExist=1 that means the value exist.otherwise not. create a method to call this procedure and go on... Happy Coding