打开数据集，计数记录并将数字返回变量的最快方法

Question

I'm pretty new to C#/WPF/SQLite and have created a form that will need to display several calculations (from two different tables). I'd like to know what you guys think the fastest way to do this would be (and if anyone could provide a rough guide for the code - it would be a big help).

It's a bit rough (and not fully working), but here it is:

    string cs = ClsVariables.StrDb;
    using(SQLiteConnection con = new SQLiteConnection(cs))
    {
        con.Open();
        string stm = "SELECT [ID] FROM tblActivities WHERE [Activity]='Sleeping'";
        using (SQLiteCommand cmd = new SQLiteCommand(stm, con))
        {
            //I'm guessing this is where I need count the number of rows (but haven't figure that bit out just yet
        }
        con.Close();   
     }

Answer 1

The aggregate function COUNT of SQL could solve you problem, but on the C# code you don't need to fill a dataset with a table and then count the rows found. Neither you need a SQLiteDateReader because when you expect your result to be just one row with only one column you use ExecuteScalar

string cmdText = "SELECT COUNT(ID) FROM tblActivities WHERE [Activity] = 'Sleeping'";
using(SQLiteConnection con = new SQLiteConnection(cs))
using(SQLiteCommand cmd = new SQLiteCommand(cmdText, con))
{
    con.Open();
    int count = Convert.ToInt32(cmd.ExecuteScalar());
    Console.WriteLine("You have " + count.ToString() + " records sleeping");
}

A last note on ExecuteScalar. It could return NULL but, in your case (COUNT returns zero or a number > 0), this is not possible so I don't check the return value for null and I directly convert it to an integer

Answer 2

You can get the count of the dataset by adding the count as a column in your query:

    int count = 0;
    using(SQLiteConnection con = new SQLiteConnection(cs))
    {
        con.Open();
        string stm = "select count(id) as count from tblActivities WHERE [Activity] = 'Sleeping'";
        using (SQLiteCommand cmd = new SQLiteCommand(stm, con))
        {
            using (IDataReader reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    if (reader["count"] != DBNull.Value && reader["count"] != null)
                    {
                        if (!int.TryParse(reader["count"], out count))
                        {
                            //failed to parse
                        }
                    }
                 }
            }
        }
        con.Close();   
     }