在C#中把两个DataTable连接起来，相当于Sql的Inner Join方法

在下面的例子中实现了3个Join方法，其目的是把两个DataTable连接起来，相当于Sql的Inner Join方法，返回DataTable的所有列。
如果两个DataTable中的DataColumn有重复的话，把第二个设置为ColumnName+"_Second",下面是代码，希望对大家有所帮助。

namespace WindowsApplication1
{
public class SQLOps
{
public SQLOps()
{
}

public static DataTable Join (DataTable First, DataTable Second, DataColumn[] FJC, DataColumn[] SJC)

{

//创建一个新的DataTable

DataTable table = new DataTable("Join");

// Use a DataSet to leverage DataRelation

using(DataSet ds = new DataSet())

{

//把DataTable Copy到DataSet中

ds.Tables.AddRange(new DataTable[]{First.Copy(),Second.Copy()});

DataColumn[] parentcolumns = new DataColumn[FJC.Length];

for(int i = 0; i < parentcolumns.Length; i++)

{

parentcolumns[i] = ds.Tables[0].Columns[FJC[i].ColumnName];

}

DataColumn[] childcolumns = new DataColumn[SJC.Length];

for(int i = 0; i < childcolumns.Length; i++)

{

childcolumns[i] = ds.Tables[1].Columns[SJC[i].ColumnName];

}

//创建关联

DataRelation r = new DataRelation(string.Empty,parentcolumns,childcolumns,false);

ds.Relations.Add(r);

//为关联表创建列

for(int i = 0; i < First.Columns.Count; i++)

{

table.Columns.Add(First.Columns[i].ColumnName, First.Columns[i].DataType);

}

for(int i = 0; i < Second.Columns.Count; i++)

{

//看看有没有重复的列，如果有在第二个DataTable的Column的列明后加_Second

if(!table.Columns.Contains(Second.Columns[i].ColumnName))

table.Columns.Add(Second.Columns[i].ColumnName, Second.Columns[i].DataType);

else

table.Columns.Add(Second.Columns[i].ColumnName + "_Second", Second.Columns[i].DataType);

}

table.BeginLoadData();

foreach(DataRow firstrow in ds.Tables[0].Rows)

{

//得到行的数据

DataRow[] childrows = firstrow.GetChildRows(r);

if(childrows != null && childrows.Length > 0)

{

object[] parentarray = firstrow.ItemArray;

foreach(DataRow secondrow in childrows)

{

object[] secondarray = secondrow.ItemArray;

object[] joinarray = new object[parentarray.Length+secondarray.Length];

Array.Copy(parentarray,0,joinarray,0,parentarray.Length);

Array.Copy(secondarray,0,joinarray,parentarray.Length,secondarray.Length);

table.LoadDataRow(joinarray,true);

}

}

}

table.EndLoadData();

}

return table;

}

public static DataTable Join (DataTable First, DataTable Second, DataColumn FJC, DataColumn SJC)

{

return Join(First, Second, new DataColumn[]{FJC}, new DataColumn[]{SJC});

}

public static DataTable Join (DataTable First, DataTable Second, string FJC, string SJC)

{

return Join(First, Second, new DataColumn[]{First.Columns[FJC]}, new DataColumn[]{First.Columns[SJC]});

}

}
}