.net中除正则之外的 用于筛选行、计算列中的值或创建聚合列 可用于表中

.net中除正则以外的 用于筛选行、计算列中的值或创建聚合列 可用于表中
JScript

Public Property Expression As String    Get    Set

Public Property Expression As StringGetSet

public string Expression { get; set; }

public string Expression { get; set; }

public:property String^ Expression {    String^ get ();    void set (String^ value);}

public:property String^ Expression {String^ get ();void set (String^ value);}

member Expression : string with get, set

member Expression : string with get, set

..::. String
用来计算列的值，或创建聚合列的表达式。表达式的返回类型由列的 DataType 来确定。

 DataSet1.Tables("Orders").Columns("OrderCount").Expression = "Count(OrderID)"

说明

如果在表达式中使用了某个列，则该表达式就存在一个对该列的依赖项。重命名或移除依赖列时不会引发异常。当访问缺少了依赖项的表达式列时，将引发异常。

在为筛选器创建表达式时，用单引号将字符串括起来：

"LastName = 'Jones'"

如果列名称包含任何非字母数字字符、以数字开头或匹配（不分大小写）以下任意的保留字，则它需要特殊处理，如下面的段落中所述。

与

之间

子级

False

隶属

Is

Like

Not

Null

Or

父级

True

如果列名称满足上述条件之一，则它必须被包括在方括号中或在“`”（重音符）引号中。例如，若要在表达式中使用名为“Column#”的列，应写成“[Column#]”：

Total * [Column#]

或 "`列号`"：

Total * `Column#`

如果列名称括在方括号中，则必须通过在所有“]”和“\”字符（不是任何其他字符）前添加反斜杠（“\”）字符来跳过这些字符。如果列名称括在重音字符中，则它不能包含任何重音字符。例如，名为“Column[]\”的列应写成：

Total * [Column[\]\\]

或

Total * `Column[]\`

说明

如果使用一个表来创建聚合，将没有组合功能。相反，所有行都在列中显示相同的值。

如果表没有行，聚合函数将返回 nullNothingnullptrnull 引用（在 Visual Basic 中为 Nothing） 。

数据类型总是可以通过检查列的 DataType 属性来确定。 还可以使用 Convert 函数来转换数据类型，如下面这一部分所示。

nullNothingnullptrnull 引用（在 Visual Basic 中为 Nothing） ，则返回 说明

可以向 C++F#JScript

Private Sub CalcColumns()     Dim rate As Single = .0862     dim table as DataTable = New DataTable      ' Create the first column.     Dim priceColumn As DataColumn = New DataColumn     With priceColumn         .DataType = System.Type.GetType("System.Decimal")         .ColumnName = "price"         .DefaultValue = 50     End With     ' Create the second, calculated, column.     Dim taxColumn As DataColumn = New DataColumn     With taxColumn         .DataType = System.Type.GetType("System.Decimal")         .ColumnName = "tax"         .Expression = "price * 0.0862"     End With    ' Create third column     Dim totalColumn As DataColumn = New DataColumn     With totalColumn         .DataType = System.Type.GetType("System.Decimal")         .ColumnName = "total"         .Expression = "price + tax"     End With     ' Add columns to DataTable     With table.Columns         .Add(priceColumn)         .Add(taxColumn)         .Add(totalColumn)     End With     Dim row As DataRow= table.NewRow     table.Rows.Add(row)     Dim view As New DataView     view.Table = table     DataGrid1.DataSource = view End Sub

Private Sub CalcColumns()     Dim rate As Single = .0862     dim table as DataTable = New DataTable      ' Create the first column.     Dim priceColumn As DataColumn = New DataColumn     With priceColumn         .DataType = System.Type.GetType("System.Decimal")         .ColumnName = "price"         .DefaultValue = 50     End With     ' Create the second, calculated, column.     Dim taxColumn As DataColumn = New DataColumn     With taxColumn         .DataType = System.Type.GetType("System.Decimal")         .ColumnName = "tax"         .Expression = "price * 0.0862"     End With    ' Create third column     Dim totalColumn As DataColumn = New DataColumn     With totalColumn         .DataType = System.Type.GetType("System.Decimal")         .ColumnName = "total"         .Expression = "price + tax"     End With     ' Add columns to DataTable     With table.Columns         .Add(priceColumn)         .Add(taxColumn)         .Add(totalColumn)     End With     Dim row As DataRow= table.NewRow     table.Rows.Add(row)     Dim view As New DataView     view.Table = table     DataGrid1.DataSource = view End Sub

private void CalcColumns(){    DataTable table = new DataTable ();    // Create the first column.    DataColumn priceColumn = new DataColumn();    priceColumn.DataType = System.Type.GetType("System.Decimal");    priceColumn.ColumnName = "price";    priceColumn.DefaultValue = 50;    // Create the second, calculated, column.    DataColumn taxColumn = new DataColumn();    taxColumn.DataType = System.Type.GetType("System.Decimal");    taxColumn.ColumnName = "tax";    taxColumn.Expression = "price * 0.0862";    // Create third column.    DataColumn totalColumn = new DataColumn();    totalColumn.DataType = System.Type.GetType("System.Decimal");    totalColumn.ColumnName = "total";    totalColumn.Expression = "price + tax";    // Add columns to DataTable.    table.Columns.Add(priceColumn);    table.Columns.Add(taxColumn);    table.Columns.Add(totalColumn);    DataRow row = table.NewRow();    table.Rows.Add(row);    DataView view = new DataView(table);    dataGrid1.DataSource = view;}

private void CalcColumns(){    DataTable table = new DataTable ();    // Create the first column.    DataColumn priceColumn = new DataColumn();    priceColumn.DataType = System.Type.GetType("System.Decimal");    priceColumn.ColumnName = "price";    priceColumn.DefaultValue = 50;    // Create the second, calculated, column.    DataColumn taxColumn = new DataColumn();    taxColumn.DataType = System.Type.GetType("System.Decimal");    taxColumn.ColumnName = "tax";    taxColumn.Expression = "price * 0.0862";    // Create third column.    DataColumn totalColumn = new DataColumn();    totalColumn.DataType = System.Type.GetType("System.Decimal");    totalColumn.ColumnName = "total";    totalColumn.Expression = "price + tax";    // Add columns to DataTable.    table.Columns.Add(priceColumn);    table.Columns.Add(taxColumn);    table.Columns.Add(totalColumn);    DataRow row = table.NewRow();    table.Rows.Add(row);    DataView view = new DataView(table);    dataGrid1.DataSource = view;}

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