datatable.select distinct

 /// <summary>
    /// 返回执行Select distinct后的DataTable
    /// </summary>
    /// <param name="SourceTable">源数据表</param>
    /// <param name="FieldNames">字段集</param>
    /// <returns></returns>
    private DataTable SelectDistinct(DataTable SourceTable, params string[] FieldNames)
    {
        object[] lastValues;
        DataTable newTable;
        DataRow[] orderedRows;

        if (FieldNames == null || FieldNames.Length == 0)
            throw new ArgumentNullException("FieldNames");

        lastValues = new object[FieldNames.Length];
        newTable = new DataTable();

        foreach (string fieldName in FieldNames)
            newTable.Columns.Add(fieldName, SourceTable.Columns[fieldName].DataType);

        orderedRows = SourceTable.Select("", string.Join(",", FieldNames));

        foreach (DataRow row in orderedRows)
        {
            if (!fieldValuesAreEqual(lastValues, row, FieldNames))
            {
                newTable.Rows.Add(createRowClone(row, newTable.NewRow(), FieldNames));

                setLastValues(lastValues, row, FieldNames);
            }
        }

        return newTable;
    }

    private bool fieldValuesAreEqual(object[] lastValues, DataRow currentRow, string[] fieldNames)
    {
        bool areEqual = true;

        for (int i = 0; i < fieldNames.Length; i++)
        {
            if (lastValues[i] == null || !lastValues[i].Equals(currentRow[fieldNames[i]]))
            {
                areEqual = false;
                break;
            }
        }

        return areEqual;
    }

    private DataRow createRowClone(DataRow sourceRow, DataRow newRow, string[] fieldNames)
    {
        foreach (string field in fieldNames)
            newRow[field] = sourceRow[field];

        return newRow;
    }

    private void setLastValues(object[] lastValues, DataRow sourceRow, string[] fieldNames)
    {
        for (int i = 0; i < fieldNames.Length; i++)
            lastValues[i] = sourceRow[fieldNames[i]];
    }

datatable.select

    public DataTable FillTable(string M_where, DataTable m_table)
    {
        DataTable _temp = m_table.Clone();
        DataRow[] _row = m_table.Select(M_where);

        foreach (DataRow _r in _row)
        {

            _temp.Rows.Add(_r.ItemArray);
        }
        return _temp;
    }

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