可不可以从datatable中选出某一列不重复的数据。

crystalreport20xx 2006-01-10 03:34:41

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liusujian02 2006-04-17

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收藏一下

crystalreport20xx 2006-01-13

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谢谢，揭帖

lidong6 2006-01-12

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这里有一个取distinct数据的方法.

static DataTable SelectDistinct(string ReturnTableName, DataTable SourceTable, string ReturnFieldName, string AdditionalFilterExpression)
{
DataTable dt = new DataTable(ReturnTableName);
dt.Columns.Add(ReturnFieldName, SourceTable.Columns[ReturnFieldName].DataType);
object LastValue = null;
foreach (DataRow dr in SourceTable.Select("", ReturnFieldName))
{
if (LastValue == null || !(ColumnEqual(LastValue, dr[ReturnFieldName])))
{
LastValue = dr[ReturnFieldName];
dt.Rows.Add(new object[] { LastValue });
}
}
if (ds != null)
ds.Tables.Add(dt);
return dt;
}

static bool ColumnEqual(object A, object B)
{
// Compares two values to see if they are equal. Also compares DBNULL.Value.
// Note: If your DataTable contains object fields, then you must extend this
// function to handle them in a meaningful way if you intend to group on them.

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
}

crystalreport20xx 2006-01-11

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但是那样做的话，就选不出那些重复的了。
我的意思是说要像sql语句中的distinct一样

califord 2006-01-10

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呵呵，学习，知道了，多学了一点

真相重于对错 2006-01-10

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DataTable.Select 方法 [C#]请参见
DataTable 类 | DataTable 成员 | System.Data 命名空间 | 代码：查询数据表 (Visual Basic) | C++ 托管扩展编程语言
C#

C++

JScript

Visual Basic

全部显示
获取 DataRow 对象的数组。
重载列表
获取所有 DataRow 对象的数组。
受 .NET Framework 精简版的支持。
[Visual Basic] Overloads Public Function Select() As DataRow()
[C#] public DataRow[] Select();
[C++] public: DataRow* Select() [];
[JScript] public function Select() : DataRow[];
按照主键顺序（如果没有主键，则按照添加顺序）获取与筛选条件相匹配的所有 DataRow 对象的数组。
受 .NET Framework 精简版的支持。
[Visual Basic] Overloads Public Function Select(String) As DataRow()
[C#] public DataRow[] Select(string);
[C++] public: DataRow* Select(String*) [];
[JScript] public function Select(String) : DataRow[];
获取按照指定的排序顺序且与筛选条件相匹配的所有 DataRow 对象的数组。
受 .NET Framework 精简版的支持。
[Visual Basic] Overloads Public Function Select(String, String) As DataRow()
[C#] public DataRow[] Select(string, string);
[C++] public: DataRow* Select(String*, String*) [];
[JScript] public function Select(String, String) : DataRow[];
获取与排序顺序中的筛选器以及指定的状态相匹配的所有 DataRow 对象的数组。
受 .NET Framework 精简版的支持。
[Visual Basic] Overloads Public Function Select(String, String, DataViewRowState) As DataRow()
[C#] public DataRow[] Select(string, string, DataViewRowState);
[C++] public: DataRow* Select(String*, String*, DataViewRowState) [];
[JScript] public function Select(String, String, DataViewRowState) : DataRow[];
示例
[Visual Basic, C#] 以下示例使用筛选表达式和记录状态来返回 DataRow 对象的数组。
[Visual Basic, C#] 注意此示例显示如何使用 Select 的一个重载版本。有关其他可用示例，请参阅单独的重载主题。
[Visual Basic]
Private Sub GetRowsByFilter()

Dim customerTable As DataTable
customerTable = new DataTable( "Customers" )

' Add columns
customerTable.Columns.Add( "id", GetType(Integer) )
customerTable.Columns.Add( "name", GetType(String) )

' Set PrimaryKey
customerTable.Columns("id").Unique = true
customerTable.PrimaryKey = new DataColumn() { customerTable.Columns("id") }

' add ten rows
Dim id As Integer
For id = 1 To 10
customerTable.Rows.Add( _
new object() { id, string.Format("customer{0}", id) } )
Next id
customerTable.AcceptChanges()

' add another ten rows
For id = 11 To 20
customerTable.Rows.Add( _
new object() { id, string.Format("customer{0}", id) } )
Next id

Dim strExpr As String
Dim strSort As String

strExpr = "id > 5"
' Sort descending by CompanyName column.
strSort = "name DESC"
' Use the Select method to find all rows matching the filter.
Dim foundRows As DataRow() = _
customerTable.Select( strExpr, strSort, DataViewRowState.Added )

PrintRows( foundRows, "filtered rows")

foundRows = customerTable.Select()
PrintRows( foundRows, "all rows")
End Sub

Private Sub PrintRows( rows() As DataRow, label As String)
Console.WriteLine( "\n{0}", label )
If rows.Length <= 0 Then
Console.WriteLine( "no rows found" )
Exit Sub
End If
Dim r As DataRow
Dim c As DataColumn
For Each r In rows
For Each c In r.Table.Columns
Console.Write( "\t {0}", r(c) )
Next c
Console.WriteLine()
Next r
End Sub
[C#]
private static void GetRowsByFilter()
{

DataTable customerTable = new DataTable( "Customers" );
// Add columns
customerTable.Columns.Add( "id", typeof(int) );
customerTable.Columns.Add( "name", typeof(string) );

// Set PrimaryKey
customerTable.Columns[ "id" ].Unique = true;
customerTable.PrimaryKey = new DataColumn[] { customerTable.Columns["id"] };

// Add ten rows
for( int id=1; id<=10; id++ )
{
customerTable.Rows.Add(
new object[] { id, string.Format("customer{0}", id) } );
}
customerTable.AcceptChanges();

// Add another ten rows
for( int id=11; id<=20; id++ )
{
customerTable.Rows.Add(
new object[] { id, string.Format("customer{0}", id) } );
}

string strExpr;
string strSort;

strExpr = "id > 5";
// Sort descending by column named CompanyName.
strSort = "name DESC";
// Use the Select method to find all rows matching the filter.
DataRow[] foundRows =
customerTable.Select( strExpr, strSort, DataViewRowState.Added );

PrintRows( foundRows, "filtered rows" );

foundRows = customerTable.Select();
PrintRows( foundRows, "all rows" );
}

private static void PrintRows( DataRow[] rows, string label )
{
Console.WriteLine( "\n{0}", label );
if( rows.Length <= 0 )
{
Console.WriteLine( "no rows found" );
return;
}
foreach( DataRow r in rows )
{
foreach( DataColumn c in r.Table.Columns )
{
Console.Write( "\t {0}", r[c] );
}
Console.WriteLine();
}
}

lidong6 2006-01-10

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marysxj(小丸子) :
楼主用的是DataTable 啊.

hdt(倦怠) ( ) :
能不能给解释一下.

marysxj 2006-01-10

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可以。
string myStr="";
for(int i=0;i<dg.Items.Count;i++)
{
if(myStr.IndexOf(dg.Items[i].cells[你要的列].Text)<0)
{
myStr+=dg.Items[i].cells[你要的列].Text+",";
}
}

最后得到的myStr就是你需要的不重复的数据。
该程序没有经过测试，你自己再改改。

真相重于对错 2006-01-10