c# datatable.select() group by 和 DataTable中进行Distinct、Group by、Join、Create

最新推荐文章于 2025-03-31 09:30:00 发布

转载最新推荐文章于 2025-03-31 09:30:00 发布 · 1.5w 阅读

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#join #c# #string #dataset #null #object

本文详细介绍了如何使用C#语言结合System.Data命名空间进行数据表(DataTable)的操作，包括创建、分组、连接等常用功能，并通过实例展示了如何实现数据的筛选、聚合与合并。适用于数据处理与分析领域的开发者。

DataTable dt = new DataTable(); dt.Columns.Add("A"); dt.Columns.Add("B"); dt.Columns.Add("C"); dt.Rows.Add("a1", "b1", "c1"); dt.Rows.Add("a1", "b2", "c2"); dt.Rows.Add("a2", "b3", "c3"); dt.Rows.Add("a3", "b4", "c4"); dt.Rows.Add("a1", "b5", "c5"); dt.Rows.Add("a2", "b6", "c6"); IEnumerable<IGrouping<string, DataRow>> result = dt.Rows.Cast<DataRow>().GroupBy<DataRow, string>(dr => dr["A"].ToString());//按A分组 foreach (IGrouping<string, DataRow> ig in result) { Console.WriteLine("当A="+ig.Key + "："); Console.WriteLine("A".PadRight(10) + "B".PadRight(10) + "C".PadRight(10)); Console.WriteLine("=====".PadRight(10) + "=====".PadRight(10) + "=====".PadRight(10)); foreach (var dr in ig) Console.WriteLine(dr["A"].ToString().PadRight(10) + dr["B"].ToString().PadRight(10) + dr["C"].ToString().PadRight(10)); }

微软知识库里面有个DataSetHelper ，可以对DataSet中的DataTable进行Distinct、Group by、Join和Create。

using System; using System.Collections; using System.Data; namespace Common { /**//**//**//// <summary> /// DataSet助手 /// </summary> public class DataSetHelper { private class FieldInfo { public string RelationName; public string FieldName; public string FieldAlias; public string Aggregate; } private DataSet ds; private ArrayList m_FieldInfo; private string m_FieldList; private ArrayList GroupByFieldInfo; private string GroupByFieldList; public DataSet DataSet { get { return ds; } } ConstructionConstruction#region Construction public DataSetHelper() { ds = null; } public DataSetHelper(ref DataSet dataSet) { ds = dataSet; } #endregion Private MethodsPrivate Methods#region Private Methods private bool ColumnEqual(object objectA, object objectB) { if ( objectA == DBNull.Value && objectB == DBNull.Value ) { return true; } if ( objectA == DBNull.Value || objectB == DBNull.Value ) { return false; } return ( objectA.Equals( objectB ) ); } private bool RowEqual(DataRow rowA, DataRow rowB, DataColumnCollection columns) { bool result = true; for ( int i = 0; i < columns.Count; i++ ) { result &= ColumnEqual( rowA[ columns[ i ].ColumnName ], rowB[ columns[ i ].ColumnName ] ); } return result; } private void ParseFieldList(string fieldList, bool allowRelation) { if ( m_FieldList == fieldList ) { return; } m_FieldInfo = new ArrayList(); m_FieldList = fieldList; FieldInfo Field; string[] FieldParts; string[] Fields = fieldList.Split( ',' ); for ( int i = 0; i <= Fields.Length - 1; i++ ) { Field = new FieldInfo(); FieldParts = Fields[ i ].Trim().Split( ' ' ); switch ( FieldParts.Length ) { case 1: //to be set at the end of the loop break; case 2: Field.FieldAlias = FieldParts[ 1 ]; break; default: return; } FieldParts = FieldParts[ 0 ].Split( '.' ); switch ( FieldParts.Length ) { case 1: Field.FieldName = FieldParts[ 0 ]; break; case 2: if ( allowRelation == false ) { return; } Field.RelationName = FieldParts[ 0 ].Trim(); Field.FieldName = FieldParts[ 1 ].Trim(); break; default: return; } if ( Field.FieldAlias == null ) { Field.FieldAlias = Field.FieldName; } m_FieldInfo.Add( Field ); } } private DataTable CreateTable(string tableName, DataTable sourceTable, string fieldList) { DataTable dt; if ( fieldList.Trim() == "" ) { dt = sourceTable.Clone(); dt.TableName = tableName; } else { dt = new DataTable( tableName ); ParseFieldList( fieldList, false ); DataColumn dc; foreach ( FieldInfo Field in m_FieldInfo ) { dc = sourceTable.Columns[ Field.FieldName ]; DataColumn column = new DataColumn(); column.ColumnName = Field.FieldAlias; column.DataType = dc.DataType; column.MaxLength = dc.MaxLength; column.Expression = dc.Expression; dt.Columns.Add( column ); } } if ( ds != null ) { ds.Tables.Add( dt ); } return dt; } private void InsertInto(DataTable destTable, DataTable sourceTable, string fieldList, string rowFilter, string sort) { ParseFieldList( fieldList, false ); DataRow[] rows = sourceTable.Select( rowFilter, sort ); DataRow destRow; foreach ( DataRow sourceRow in rows ) { destRow = destTable.NewRow(); if ( fieldList == "" ) { foreach ( DataColumn dc in destRow.Table.Columns ) { if ( dc.Expression == "" ) { destRow[ dc ] = sourceRow[ dc.ColumnName ]; } } } else { foreach ( FieldInfo field in m_FieldInfo ) { destRow[ field.FieldAlias ] = sourceRow[ field.FieldName ]; } } destTable.Rows.Add( destRow ); } } private void ParseGroupByFieldList(string FieldList) { if ( GroupByFieldList == FieldList ) { return; } GroupByFieldInfo = new ArrayList(); FieldInfo Field; string[] FieldParts; string[] Fields = FieldList.Split( ',' ); for ( int i = 0; i <= Fields.Length - 1; i++ ) { Field = new FieldInfo(); FieldParts = Fields[ i ].Trim().Split( ' ' ); switch ( FieldParts.Length ) { case 1: //to be set at the end of the loop break; case 2: Field.FieldAlias = FieldParts[ 1 ]; break; default: return; } FieldParts = FieldParts[ 0 ].Split( '(' ); switch ( FieldParts.Length ) { case 1: Field.FieldName = FieldParts[ 0 ]; break; case 2: Field.Aggregate = FieldParts[ 0 ].Trim().ToLower(); Field.FieldName = FieldParts[ 1 ].Trim( ' ', ')' ); break; default: return; } if ( Field.FieldAlias == null ) { if ( Field.Aggregate == null ) { Field.FieldAlias = Field.FieldName; } else { Field.FieldAlias = Field.Aggregate + "of" + Field.FieldName; } } GroupByFieldInfo.Add( Field ); } GroupByFieldList = FieldList; } private DataTable CreateGroupByTable(string tableName, DataTable sourceTable, string fieldList) { if ( fieldList == null || fieldList.Length == 0 ) { return sourceTable.Clone(); } else { DataTable dt = new DataTable( tableName ); ParseGroupByFieldList( fieldList ); foreach ( FieldInfo Field in GroupByFieldInfo ) { DataColumn dc = sourceTable.Columns[ Field.FieldName ]; if ( Field.Aggregate == null ) { dt.Columns.Add( Field.FieldAlias, dc.DataType, dc.Expression ); } else { dt.Columns.Add( Field.FieldAlias, dc.DataType ); } } if ( ds != null ) { ds.Tables.Add( dt ); } return dt; } } private void InsertGroupByInto(DataTable destTable, DataTable sourceTable, string fieldList, string rowFilter, string groupBy) { if ( fieldList == null || fieldList.Length == 0 ) { return; } ParseGroupByFieldList( fieldList ); ParseFieldList( groupBy, false ); DataRow[] rows = sourceTable.Select( rowFilter, groupBy ); DataRow lastSourceRow = null, destRow = null; bool sameRow; int rowCount = 0; foreach ( DataRow sourceRow in rows ) { sameRow = false; if ( lastSourceRow != null ) { sameRow = true; foreach ( FieldInfo Field in m_FieldInfo ) { if ( !ColumnEqual( lastSourceRow[ Field.FieldName ], sourceRow[ Field.FieldName ] ) ) { sameRow = false; break; } } if ( !sameRow ) { destTable.Rows.Add( destRow ); } } if ( !sameRow ) { destRow = destTable.NewRow(); rowCount = 0; } rowCount += 1; foreach ( FieldInfo field in GroupByFieldInfo ) { switch ( field.Aggregate.ToLower() ) { case null: case "": case "last": destRow[ field.FieldAlias ] = sourceRow[ field.FieldName ]; break; case "first": if ( rowCount == 1 ) { destRow[ field.FieldAlias ] = sourceRow[ field.FieldName ]; } break; case "count": destRow[ field.FieldAlias ] = rowCount; break; case "sum": destRow[ field.FieldAlias ] = Add( destRow[ field.FieldAlias ], sourceRow[ field.FieldName ] ); break; case "max": destRow[ field.FieldAlias ] = Max( destRow[ field.FieldAlias ], sourceRow[ field.FieldName ] ); break; case "min": if ( rowCount == 1 ) { destRow[ field.FieldAlias ] = sourceRow[ field.FieldName ]; } else { destRow[ field.FieldAlias ] = Min( destRow[ field.FieldAlias ], sourceRow[ field.FieldName ] ); } break; } } lastSourceRow = sourceRow; } if ( destRow != null ) { destTable.Rows.Add( destRow ); } } private object Min(object a, object b) { if ( ( a is DBNull ) || ( b is DBNull ) ) { return DBNull.Value; } if ( ( (IComparable) a ).CompareTo( b ) == -1 ) { return a; } else { return b; } } private object Max(object a, object b) { if ( a is DBNull ) { return b; } if ( b is DBNull ) { return a; } if ( ( (IComparable) a ).CompareTo( b ) == 1 ) { return a; } else { return b; } } private object Add(object a, object b) { if ( a is DBNull ) { return b; } if ( b is DBNull ) { return a; } return ( (decimal) a + (decimal) b ); } private DataTable CreateJoinTable(string tableName, DataTable sourceTable, string fieldList) { if ( fieldList == null ) { return sourceTable.Clone(); } else { DataTable dt = new DataTable( tableName ); ParseFieldList( fieldList, true ); foreach ( FieldInfo field in m_FieldInfo ) { if ( field.RelationName == null ) { DataColumn dc = sourceTable.Columns[ field.FieldName ]; dt.Columns.Add( dc.ColumnName, dc.DataType, dc.Expression ); } else { DataColumn dc = sourceTable.ParentRelations[ field.RelationName ].ParentTable.Columns[ field.FieldName ]; dt.Columns.Add( dc.ColumnName, dc.DataType, dc.Expression ); } } if ( ds != null ) { ds.Tables.Add( dt ); } return dt; } } private void InsertJoinInto(DataTable destTable, DataTable sourceTable, string fieldList, string rowFilter, string sort) { if ( fieldList == null ) { return; } else { ParseFieldList( fieldList, true ); DataRow[] Rows = sourceTable.Select( rowFilter, sort ); foreach ( DataRow SourceRow in Rows ) { DataRow DestRow = destTable.NewRow(); foreach ( FieldInfo Field in m_FieldInfo ) { if ( Field.RelationName == null ) { DestRow[ Field.FieldName ] = SourceRow[ Field.FieldName ]; } else { DataRow ParentRow = SourceRow.GetParentRow( Field.RelationName ); DestRow[ Field.FieldName ] = ParentRow[ Field.FieldName ]; } } destTable.Rows.Add( DestRow ); } } } #endregion SelectDistinct / DistinctSelectDistinct / Distinct#region SelectDistinct / Distinct /**//**//**//// <summary> /// 按照fieldName从sourceTable中选择出不重复的行， /// 相当于select distinct fieldName from sourceTable /// </summary> /// <param name="tableName">表名</param> /// <param name="sourceTable">源DataTable</param> /// <param name="fieldName">列名</param> /// <returns>一个新的不含重复行的DataTable，列只包括fieldName指明的列</returns> 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.Contains( tableName ) ) { ds.Tables.Add( dt ); } return dt; } /**//**//**//// <summary> /// 按照fieldName从sourceTable中选择出不重复的行， /// 相当于select distinct fieldName1,fieldName2,,fieldNamen from sourceTable /// </summary> /// <param name="tableName">表名</param> /// <param name="sourceTable">源DataTable</param> /// <param name="fieldNames">列名数组</param> /// <returns>一个新的不含重复行的DataTable，列只包括fieldNames中指明的列</returns> public DataTable SelectDistinct(string tableName, DataTable sourceTable, string[] fieldNames) { DataTable dt = new DataTable( tableName ); object[] values = new object[fieldNames.Length]; string fields = ""; for ( int i = 0; i < fieldNames.Length; i++ ) { dt.Columns.Add( fieldNames[ i ], sourceTable.Columns[ fieldNames[ i ] ].DataType ); fields += fieldNames[ i ] + ","; } fields = fields.Remove( fields.Length - 1, 1 ); DataRow lastRow = null; foreach ( DataRow dr in sourceTable.Select( "", fields ) ) { if ( lastRow == null || !( RowEqual( lastRow, dr, dt.Columns ) ) ) { lastRow = dr; for ( int i = 0; i < fieldNames.Length; i++ ) { values[ i ] = dr[ fieldNames[ i ] ]; } dt.Rows.Add( values ); } } if ( ds != null && !ds.Tables.Contains( tableName ) ) { ds.Tables.Add( dt ); } return dt; } /**//**//**//// <summary> /// 按照fieldName从sourceTable中选择出不重复的行， /// 并且包含sourceTable中所有的列。 /// </summary> /// <param name="tableName">表名</param> /// <param name="sourceTable">源表</param> /// <param name="fieldName">字段</param> /// <returns>一个新的不含重复行的DataTable</returns> public DataTable Distinct(string tableName, DataTable sourceTable, string fieldName) { DataTable dt = sourceTable.Clone(); dt.TableName = tableName; object lastValue = null; foreach ( DataRow dr in sourceTable.Select( "", fieldName ) ) { if ( lastValue == null || !( ColumnEqual( lastValue, dr[ fieldName ] ) ) ) { lastValue = dr[ fieldName ]; dt.Rows.Add( dr.ItemArray ); } } if ( ds != null && !ds.Tables.Contains( tableName ) ) { ds.Tables.Add( dt ); } return dt; } /**//**//**//// <summary> /// 按照fieldNames从sourceTable中选择出不重复的行， /// 并且包含sourceTable中所有的列。 /// </summary> /// <param name="tableName">表名</param> /// <param name="sourceTable">源表</param> /// <param name="fieldNames">字段</param> /// <returns>一个新的不含重复行的DataTable</returns> public DataTable Distinct(string tableName, DataTable sourceTable, string[] fieldNames) { DataTable dt = sourceTable.Clone(); dt.TableName = tableName; string fields = ""; for ( int i = 0; i < fieldNames.Length; i++ ) { fields += fieldNames[ i ] + ","; } fields = fields.Remove( fields.Length - 1, 1 ); DataRow lastRow = null; foreach ( DataRow dr in sourceTable.Select( "", fields ) ) { if ( lastRow == null || !( RowEqual( lastRow, dr, dt.Columns ) ) ) { lastRow = dr; dt.Rows.Add( dr.ItemArray ); } } if ( ds != null && !ds.Tables.Contains( tableName ) ) { ds.Tables.Add( dt ); } return dt; } #endregion Select Table IntoSelect Table Into#region Select Table Into /**//**//**//// <summary> /// 按sort排序，按rowFilter过滤sourceTable， /// 复制fieldList中指明的字段的数据到新DataTable，并返回之 /// </summary> /// <param name="tableName">表名</param> /// <param name="sourceTable">源表</param> /// <param name="fieldList">字段列表</param> /// <param name="rowFilter">过滤条件</param> /// <param name="sort">排序</param> /// <returns>新DataTable</returns> public DataTable SelectInto(string tableName, DataTable sourceTable, string fieldList, string rowFilter, string sort) { DataTable dt = CreateTable( tableName, sourceTable, fieldList ); InsertInto( dt, sourceTable, fieldList, rowFilter, sort ); return dt; } #endregion Group By TableGroup By Table#region Group By Table public DataTable SelectGroupByInto(string tableName, DataTable sourceTable, string fieldList, string rowFilter, string groupBy) { DataTable dt = CreateGroupByTable( tableName, sourceTable, fieldList ); InsertGroupByInto( dt, sourceTable, fieldList, rowFilter, groupBy ); return dt; } #endregion Join TablesJoin Tables#region Join Tables public DataTable SelectJoinInto(string tableName, DataTable sourceTable, string fieldList, string rowFilter, string sort) { DataTable dt = CreateJoinTable( tableName, sourceTable, fieldList ); InsertJoinInto( dt, sourceTable, fieldList, rowFilter, sort ); return dt; } #endregion Create TableCreate Table#region Create Table public DataTable CreateTable(string tableName, string fieldList) { DataTable dt = new DataTable( tableName ); DataColumn dc; string[] Fields = fieldList.Split( ',' ); string[] FieldsParts; string Expression; foreach ( string Field in Fields ) { FieldsParts = Field.Trim().Split( " ".ToCharArray(), 3 ); // allow for spaces in the expression // add fieldname and datatype if ( FieldsParts.Length == 2 ) { dc = dt.Columns.Add( FieldsParts[ 0 ].Trim(), Type.GetType( "System." + FieldsParts[ 1 ].Trim(), true, true ) ); dc.AllowDBNull = true; } else if ( FieldsParts.Length == 3 ) // add fieldname, datatype, and expression { Expression = FieldsParts[ 2 ].Trim(); if ( Expression.ToUpper() == "REQUIRED" ) { dc = dt.Columns.Add( FieldsParts[ 0 ].Trim(), Type.GetType( "System." + FieldsParts[ 1 ].Trim(), true, true ) ); dc.AllowDBNull = false; } else { dc = dt.Columns.Add( FieldsParts[ 0 ].Trim(), Type.GetType( "System." + FieldsParts[ 1 ].Trim(), true, true ), Expression ); } } else { return null; } } if ( ds != null ) { ds.Tables.Add( dt ); } return dt; } public DataTable CreateTable(string tableName, string fieldList, string keyFieldList) { DataTable dt = CreateTable( tableName, fieldList ); string[] KeyFields = keyFieldList.Split( ',' ); if ( KeyFields.Length > 0 ) { DataColumn[] KeyFieldColumns = new DataColumn[KeyFields.Length]; int i; for ( i = 1; i == KeyFields.Length - 1; ++i ) { KeyFieldColumns[ i ] = dt.Columns[ KeyFields[ i ].Trim() ]; } dt.PrimaryKey = KeyFieldColumns; } return dt; } #endregion }