[英]Is there an easy way to INNER join , OUTER join , LEFT OUTER join, RIGHT OUTER join, or UNION two (or more) DataTables in C#?
[英]How to Left Outer Join two DataTables in c#?
我如何保持左外連接(我認為它是左外連接但我不是100%確定)兩個數據表具有以下表和條件,同時保留兩個表中的所有列?
dtblLeft:
id col1 anotherColumn2
1 1 any2
2 1 any2
3 2 any2
4 3 any2
5 3 any2
6 3 any2
7 any2
dtblRight:
col1 col2 anotherColumn1
1 Hi any1
2 Bye any1
3 Later any1
4 Never any1
dtblJoined:
id col1 col2 anotherColumn1 anotherColumn2
1 1 Hi any1 any2
2 1 Hi any1 any2
3 2 Bye any1 any2
4 3 Later any1 any2
5 3 Later any1 any2
6 3 Later any1 any2
7 any2
條件:
我可以使用常規的DataTable操作,LINQ或其他任何操作。
我嘗試了這個,但它刪除了重復:
dtblA.PrimaryKey = new DataColumn[] {dtblA.Columns["col1"]}
DataTable dtblJoined = new DataTable();
dtblJoined.Merge(dtblA, false, MissingSchemaAction.AddWithKey);
dtblJoined.Merge(dtblB, false, MissingSchemaAction.AddWithKey);
編輯1:
這接近我想要的但它只有一個表中的列(在此鏈接中找到):
dtblJoined = (from t1 in dtblA.Rows.Cast<DataRow>()
join t2 in dtblB.Rows.Cast<DataRow>() on t1["col1"] equals t2["col1"]
select t1).CopyToDataTable();
編輯2:
這個鏈接的答案似乎對我有用,但我不得不改變它如下:
DataTable targetTable = dtblA.Clone();
var dt2Columns = dtblB.Columns.OfType<DataColumn>().Select(dc =>
new DataColumn(dc.ColumnName, dc.DataType, dc.Expression, dc.ColumnMapping));
var dt2FinalColumns = from dc in dt2Columns.AsEnumerable()
where targetTable.Columns.Contains(dc.ColumnName) == false
select dc;
targetTable.Columns.AddRange(dt2FinalColumns.ToArray());
var rowData = from row1 in dtblA.AsEnumerable()
join row2 in dtblB.AsEnumerable()
on row1["col1"] equals row2["col1"]
select row1.ItemArray.Concat(row2.ItemArray.Where(r2 => row1.ItemArray.Contains(r2) == false)).ToArray();
foreach (object[] values in rowData)
targetTable.Rows.Add(values);
我也找到了這個鏈接 ,我可能會嘗試一下,因為它看起來更簡潔。
編輯3(11/18/2013):
更新了表格以反映更多情況。
感謝你的幫助。 以下是我基於多種資源提出的建議:
public static class DataTableHelper
{
public enum JoinType
{
/// <summary>
/// Same as regular join. Inner join produces only the set of records that match in both Table A and Table B.
/// </summary>
Inner = 0,
/// <summary>
/// Same as Left Outer join. Left outer join produces a complete set of records from Table A, with the matching records (where available) in Table B. If there is no match, the right side will contain null.
/// </summary>
Left = 1
}
/// <summary>
/// Joins the passed in DataTables on the colToJoinOn.
/// <para>Returns an appropriate DataTable with zero rows if the colToJoinOn does not exist in both tables.</para>
/// </summary>
/// <param name="dtblLeft"></param>
/// <param name="dtblRight"></param>
/// <param name="colToJoinOn"></param>
/// <param name="joinType"></param>
/// <returns></returns>
/// <remarks>
/// <para>http://stackoverflow.com/questions/2379747/create-combined-datatable-from-two-datatables-joined-with-linq-c-sharp?rq=1</para>
/// <para>http://msdn.microsoft.com/en-us/library/vstudio/bb397895.aspx</para>
/// <para>http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html</para>
/// <para>http://stackoverflow.com/questions/406294/left-join-and-left-outer-join-in-sql-server</para>
/// </remarks>
public static DataTable JoinTwoDataTablesOnOneColumn(DataTable dtblLeft, DataTable dtblRight, string colToJoinOn, JoinType joinType)
{
//Change column name to a temp name so the LINQ for getting row data will work properly.
string strTempColName = colToJoinOn + "_2";
if (dtblRight.Columns.Contains(colToJoinOn))
dtblRight.Columns[colToJoinOn].ColumnName = strTempColName;
//Get columns from dtblLeft
DataTable dtblResult = dtblLeft.Clone();
//Get columns from dtblRight
var dt2Columns = dtblRight.Columns.OfType<DataColumn>().Select(dc => new DataColumn(dc.ColumnName, dc.DataType, dc.Expression, dc.ColumnMapping));
//Get columns from dtblRight that are not in dtblLeft
var dt2FinalColumns = from dc in dt2Columns.AsEnumerable()
where !dtblResult.Columns.Contains(dc.ColumnName)
select dc;
//Add the rest of the columns to dtblResult
dtblResult.Columns.AddRange(dt2FinalColumns.ToArray());
//No reason to continue if the colToJoinOn does not exist in both DataTables.
if (!dtblLeft.Columns.Contains(colToJoinOn) || (!dtblRight.Columns.Contains(colToJoinOn) && !dtblRight.Columns.Contains(strTempColName)))
{
if (!dtblResult.Columns.Contains(colToJoinOn))
dtblResult.Columns.Add(colToJoinOn);
return dtblResult;
}
switch (joinType)
{
default:
case JoinType.Inner:
#region Inner
//get row data
//To use the DataTable.AsEnumerable() extension method you need to add a reference to the System.Data.DataSetExtension assembly in your project.
var rowDataLeftInner = from rowLeft in dtblLeft.AsEnumerable()
join rowRight in dtblRight.AsEnumerable() on rowLeft[colToJoinOn] equals rowRight[strTempColName]
select rowLeft.ItemArray.Concat(rowRight.ItemArray).ToArray();
//Add row data to dtblResult
foreach (object[] values in rowDataLeftInner)
dtblResult.Rows.Add(values);
#endregion
break;
case JoinType.Left:
#region Left
var rowDataLeftOuter = from rowLeft in dtblLeft.AsEnumerable()
join rowRight in dtblRight.AsEnumerable() on rowLeft[colToJoinOn] equals rowRight[strTempColName] into gj
from subRight in gj.DefaultIfEmpty()
select rowLeft.ItemArray.Concat((subRight== null) ? (dtblRight.NewRow().ItemArray) :subRight.ItemArray).ToArray();
//Add row data to dtblResult
foreach (object[] values in rowDataLeftOuter)
dtblResult.Rows.Add(values);
#endregion
break;
}
//Change column name back to original
dtblRight.Columns[strTempColName].ColumnName = colToJoinOn;
//Remove extra column from result
dtblResult.Columns.Remove(strTempColName);
return dtblResult;
}
}
編輯3:
此方法現在可以正常工作,當表格有2000多行時,它仍然很快。 任何建議/建議/改進將不勝感激。
編輯4:
我有一個特定的場景讓我意識到以前的版本真的在做一個內部聯接。 該功能已被修改以解決該問題。 我在這個鏈接上使用了信息來弄明白。
這只是兩個表之間的內部聯接:
var query = (from x in a.AsEnumerable()
join y in b.AsEnumerable() on x.Field<int>("col1") equals y.Field<int>("col1")
select new { col1= y.Field<int>("col1"), col2=x.Field<int>("col2") }).ToList();
生產:
col1 col2
1 Hi
1 Hi
2 Bye
3 Later
3 Later
3 Later
您可以使用LINQ並執行以下操作:
var dtblJoined = from dB in dtblB.AsEnumerable()
join dA in dtblA.AsEnumerable() on dA.col1 equals dB.col1 into dAB
from d in dAB.DefaultIfEmpty()
select new (col1 = dB.col1, ; col2 = (dB.col1 == dA.col1) ? dA.col2 : null);
這將返回一個IEnumerable,因為結果不是DataTable,但它應該讓你更接近你想要的東西。 可能需要稍微調整一下。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.