Check if a record exists in the database

Question

I am using these lines of code to check if the record exists or not.

SqlCommand check_User_Name = new SqlCommand(\"SELECT * FROM Table WHERE ([user] = \'\" +         


        

Answer 1

Use try catch:

try
{
    SqlCommand check_User_Name = new SqlCommand("SELECT * FROM Table WHERE ([user] = '" + txtBox_UserName.Text + "') ", conn);

    int UserExist = (int)check_User_Name.ExecuteScalar();
    // Update query
}
catch
{
    // Insert query
}

Answer 2

MySqlCommand cmd = new MySqlCommand("select * from table where user = '" + user.Text + "'", con);
MySqlDataAdapter da = new MySqlDataAdapter(cmd);
DataSet ds1 = new DataSet();
da.Fill(ds1);
int i = ds1.Tables[0].Rows.Count;
if (i > 0) {
    // Exist
}
else {
    // Add 
}

Answer 3

try this

 public static bool CheckUserData(string phone, string config)
    {
        string sql = @"SELECT * FROM AspNetUsers WHERE PhoneNumber = @PhoneNumber";
        using (SqlConnection conn = new SqlConnection(config)
            )
        {
            conn.Open();
            using (SqlCommand cmd = new SqlCommand(sql, conn))
            {
                cmd.Parameters.AddWithValue("@PhoneNumber", phone);
                SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                if (reader.HasRows)
                {
                    return true;  // data exist
                }
                else
                {
                    return false; //data not exist
                }
            }
        }
    }

Answer 4

I was asking myself the same question, and I found no clear answers, so I created a simple test.

I tried to add 100 rows with duplicate primary keys and measured the time needed to process it. I am using SQL Server 2014 Developer and Entity Framework 6.1.3 with a custom repository.

Dim newE As New Employee With {.Name = "e"}
For index = 1 To 100
  Dim e = employees.Select(Function(item) item.Name = "e").FirstOrDefault()
  If e Is Nothing Then
    employees.Insert(newE)
  End If
Next  

2.1 seconds

Dim newE As New Employee With {.Name = "e"}
For index = 1 To 100
  Try
    employees.Insert(newE)
  Catch ex As Exception
  End Try
Next  

3.1 seconds

Answer 5

sqlConnection.Open();
using (var sqlCommand = new SqlCommand("SELECT COUNT(*) FROM Table WHERE ([user] = '" + txtBox_UserName.Text + "'", sqlConnection))
{

    SqlDataReader reader = sqlCommand.ExecuteReader();
    if (reader.HasRows)
    {
        lblMessage.Text ="Record Already Exists.";

    }
    else
    {
        lblMessage.Text ="Record Not Exists.";
    }

    reader.Close();
    reader.Dispose();
}

sqlConnection.Close();

Answer 6

You can write as follows:

SqlCommand check_User_Name = new SqlCommand("SELECT * FROM Table WHERE ([user] = '" + txtBox_UserName.Text + "') ", conn);
if (check_User_Name.ExecuteScalar()!=null)
{
    int UserExist = (int)check_User_Name.ExecuteScalar();
    if (UserExist > 0)
    {
        //Username Exist
    }
}