将 Access 中的数据汇总到 DataTable

Question

我有一个包含 3 个定义类型的列和一个包含数字的列的数据库。 这些类型可以在数据库中多次出现。 我想创建一个 DataTable，它只显示每种类型一次并汇总与该类型相关的数字。

            List<String> types = typesInTable(table);
            DataTable t = new DataTable();
            t.Clear();
            t.Columns.Add("Type");
            t.Columns.Add("Total Expenses");

           foreach (String type in types)
            {
                DataRow tmp = t.NewRow();
                tmp["Type"] = type;
                int total = 0;
                myConnection.Open();
                OleDbDataReader reader = null;
                OleDbCommand cmd = new OleDbCommand("SELECT [Type] , [Expense] FROM [" + table+"]", myConnection);
                reader = cmd.ExecuteReader();
                while (reader.Read())
                {
                    if(reader["Type"].ToString().Equals(type))
                    {
                        total += Convert.ToInt32(reader["Expense"].ToString());
                    }
                }

                tmp["Total Expenses"] = total;
                if (!t.Rows.Contains(tmp))
                {
                    t.Rows.Add(tmp);
                }
                myConnection.Close();
            }

此代码使类型出现多次。

Answer 1

您可以使用此代码创建包含按总和分组的每种类型的 DataTable：

DataTable t = new DataTable();
myConnection.Open();
string query = string.Format("SELECT Type, Sum(Expense) AS TotalExpenses FROM [{0}] group by Type", table);
OleDbCommand cmd = new OleDbCommand(query, myConnection);
OleDbDataAdapter adapter = new OleDbDataAdapter(cmd);
adapter.Fill(t);
myConnection.Close();

如果您想在 1 个 DataTable 中汇总来自不同表的类型，请使用：

List<String> tableList = serviceMethod.getTableList();
DataTable dtAllType = new DataTable();
foreach (string table in tableList)
{
    DataTable dtTemp = new DataTable();
    myConnection.Open();
    string query = string.Format("SELECT Type, Sum(Expense) AS TotalExpenses FROM [{0}] group by Type", table);
    OleDbCommand cmd = new OleDbCommand(query, myConnection);
    OleDbDataAdapter adapter = new OleDbDataAdapter(cmd);
    adapter.Fill(dtTemp);

    for (int i = 0; i < dtTemp.Rows.Count; i++)
    {
        bool isDupe = false;
        for (int j = 0; j < dtAllType.Rows.Count; j++)
        {
            if (dtTemp.Rows[i][0].ToString() == dtAllType.Rows[j][0].ToString())
            {
                dtAllType.Rows[j][1] = int.Parse(dtAllType.Rows[j][1].ToString()) + int.Parse(dtTemp.Rows[i][1].ToString());
                isDupe = true;
                break;
            }
        }

        if (!isDupe)
        {
            dtAllType.ImportRow(dtTemp.Rows[i]);
        }
    }
    myConnection.Close();
}

dtAllTypeDataTable 包含按经验总和分组的类型