Get distinct count of rows in the DataSet
The table in the DataSet is as follows:
Column1 Column2
11 A
11 B
22 C
33 D
33 E
44 F
Distinct count of Column1 is 4 (that is 11,22,33,44), not 6. How can I get 4 ?
//此方法将所选字段的唯一值复制到一个新的 DataTable 。 如果字段包含 NULL 值，目标表中的记录还包含 NULL 值
public DataTable SelectDistinct(string TableName, DataTable SourceTable, string FieldName)
{
DataTable dt = new DataTable(TableName);
dt.Columns.Add(FieldName, SourceTable.Columns[FieldName].DataType);
object LastValue = null;
foreach (DataRow dr in SourceTable.Select("", FieldName))
{
if (LastValue == null || !(ColumnEqual(LastValue, dr[FieldName])))
{
LastValue = dr[FieldName];
dt.Rows.Add(new object[] { LastValue });
}
}
////if (ds != null)
////ds.Tables.Add(dt);
return dt;
}
static bool ColumnEqual(object A, object B)
{
if (A == DBNull.Value && B == DBNull.Value) // both are DBNull.Value
return true;
if (A == DBNull.Value || B == DBNull.Value) // only one is DBNull.Value
return false;
return (A.Equals(B)); // value type standard comparison
}
public DataTable SelectDistinct(string TableName, DataTable SourceTable, string FieldName)
{
DataTable dt = new DataTable(TableName);
dt.Columns.Add(FieldName, SourceTable.Columns[FieldName].DataType);
object LastValue = null;
foreach (DataRow dr in SourceTable.Select("", FieldName))
{
if (LastValue == null || !(ColumnEqual(LastValue, dr[FieldName])))
{
LastValue = dr[FieldName];
dt.Rows.Add(new object[] { LastValue });
}
}
////if (ds != null)
////ds.Tables.Add(dt);
return dt;
}
static bool ColumnEqual(object A, object B)
{
if (A == DBNull.Value && B == DBNull.Value) // both are DBNull.Value
return true;
if (A == DBNull.Value || B == DBNull.Value) // only one is DBNull.Value
return false;
return (A.Equals(B)); // value type standard comparison
}
http://support.microsoft.com/default.aspx?scid=kb;en-us;326176
http://weblogs.asp.net/eporter/archive/2005/02/10/370548.aspx
