?? ? ? ?///?<summary>
????????///?將所選字段的唯一值復(fù)制到一個新的?DataTable。?
????????///?<para>如果字段包含?NULL?值，目標(biāo)表中的記錄還包含?NULL?值</para>
????????///?</summary>
????????///?<param?name="sourceTable">源數(shù)據(jù)表</param>
????????///?<param?name="filterExpression">檢索條件</param>
????????///?<param?name="fieldName">唯一值的字段名</param>
????????///?<returns></returns>?
????????public?DataTable?SelectDistinct(DataTable?sourceTable,?string?filterExpression,?string?fieldName)
????????{
????????????DataTable?dt?=?new?DataTable(sourceTable.TableName);
????????????dt.Columns.Add(fieldName,?sourceTable.Columns[fieldName].DataType);

????????????object?lastValue?=?null;
????????????foreach?(DataRow?dr?in?sourceTable.Select(filterExpression,?fieldName))
????????????{
????????????????if?(lastValue?==?null?||?!(ColumnEqual(lastValue,?dr[fieldName])))
????????????????{
????????????????????lastValue?=?dr[fieldName];
????????????????????dt.Rows.Add(new?object[]?{?lastValue?});
????????????????}
????????????}
????????????return?dt;
????????}
????????private?bool?ColumnEqual(object?A,?object?B)
????????{
????????????if?(A?==?DBNull.Value?&&?B?==?DBNull.Value)
????????????????return?true;
????????????if?(A?==?DBNull.Value?||?B?==?DBNull.Value)
????????????????return?false;
????????????return?(A.Equals(B));
????????}?

?

轉(zhuǎn)載于:https://www.cnblogs.com/EasyData/archive/2010/01/20/1652173.html

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