如何在c#中左外连接两个数据表? [英] How to Left Outer Join two DataTables in c#?
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问题描述
如何在保留两个表中的所有列的同时，使用以下表和条件左外连接两个数据表?
dtblLeft:
id col1 anotherColumn21 1 任意 22 1 任意 23 2 任意 24 3 任意 25 3 任意26 3 任意27 任意 2dtblRight:
col1 col2 anotherColumn11 你好 12再见任何13 后来any14 从来没有 1dtblJoined:
id col1 col2 anotherColumn1 anotherColumn21 1 嗨 any1 any22 1 嗨 any1 any23 2 再见 any1 any24 3 后来 any1 any25 3 后来 any1 any26 3 后来 any1 any27 任意 2条件:
- 在 dtblLeft 中，col1 不需要具有唯一值.
- 在 dtblRight 中，col1 具有唯一值.
- 如果 dtblLeft 在 col1 中缺少外键，或者它有一个在 dtblRight 中不存在的外键，则将插入空字段或空字段.
- 加入 col1.
我可以使用常规的 DataTable 操作、LINQ 或其他任何操作.
我试过了，但它删除了重复项:
dtblA.PrimaryKey = new DataColumn[] {dtblA.Columns[col1"]}DataTable dtblJoined = new DataTable();dtblJoined.Merge(dtblA, false, MissingSchemaAction.AddWithKey);dtblJoined.Merge(dtblB, false, MissingSchemaAction.AddWithKey);编辑 1:
这与我想要的很接近，但它只有其中一个表中的列(可在此link ):
dtblJoined =(来自 dtblA.Rows.Cast() 中的 t1在 t1[col1"] 上的 dtblB.Rows.Cast<DataRow>() 中加入 t2 等于 t2[col1"]选择 t1).CopyToDataTable(); 编辑 2:
来自这个link 似乎对我有用，但我不得不对其进行如下更改:
DataTable targetTable = dtblA.Clone();var dt2Columns = dtblB.Columns.OfType().Select(dc =>新数据列(dc.ColumnName，dc.DataType，dc.Expression，dc.ColumnMapping))；var dt2FinalColumns = 来自 dt2Columns.AsEnumerable() 中的 dc其中 targetTable.Columns.Contains(dc.ColumnName) == false选择直流；targetTable.Columns.AddRange(dt2FinalColumns.ToArray());var rowData = from row1 in dtblA.AsEnumerable()在 dtblB.AsEnumerable() 中加入 row2在 row1[col1"] 上等于 row2[col1"]选择 row1.ItemArray.Concat(row2.ItemArray.Where(r2 => row1.ItemArray.Contains(r2) == false)).ToArray();foreach(rowData 中的对象 [] 值)targetTable.Rows.Add(values); 我还发现了这个链接 我可能会尝试一下，因为它看起来更简洁.
编辑 3 (11/18/2013):
更新了表格以反映更多情况.
解决方案
感谢大家的帮助.以下是我根据多种资源得出的结论:
公共静态类DataTableHelper{公共枚举 JoinType{///<总结>///与常规连接相同.内连接只生成在表 A 和表 B 中都匹配的记录集.///</总结>内 = 0,///<总结>///与左外连接相同.左外连接从表 A 中生成一组完整的记录，匹配的记录(如果可用)在表 B 中.如果没有匹配，右侧将包含空值.///</总结>左 = 1}///<总结>///在 colToJoinOn 上连接传入的 DataTables.///<para>如果两个表中都不存在 colToJoinOn，则返回具有零行的适当数据表.</para>///</总结>///<param name="dtblLeft"></param>///<param name="dtblRight"></param>///<param name="colToJoinOn"></param>///<param name="joinType"></param>///<returns></returns>///<备注>///<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>///</备注>公共静态数据表 JoinTwoDataTablesOnOneColumn(数据表 dtblLeft，数据表 dtblRight，字符串 colToJoinOn，JoinType joinType){//将列名更改为临时名称，以便获取行数据的 LINQ 能够正常工作.string strTempColName = colToJoinOn + "_2";如果(dtblRight.Columns.Contains(colToJoinOn))dtblRight.Columns[colToJoinOn].ColumnName = strTempColName;//从dtblLeft获取列数据表 dtblResult = dtblLeft.Clone();//从dtblRight中获取列var dt2Columns = dtblRight.Columns.OfType().Select(dc => new DataColumn(dc.ColumnName, dc.DataType, dc.Expression, dc.ColumnMapping));//从dtblRight中获取不在dtblLeft中的列var dt2FinalColumns = 来自 dt2Columns.AsEnumerable() 中的 dc其中 !dtblResult.Columns.Contains(dc.ColumnName)选择直流；//将其余的列添加到dtblResultdtblResult.Columns.AddRange(dt2FinalColumns.ToArray());//如果两个数据表中都不存在 colToJoinOn，则没有理由继续.if (!dtblLeft.Columns.Contains(colToJoinOn) || (!dtblRight.Columns.Contains(colToJoinOn) && !dtblRight.Columns.Contains(strTempColName))){如果 (!dtblResult.Columns.Contains(colToJoinOn))dtblResult.Columns.Add(colToJoinOn);返回 dtblResult;}开关(joinType){默认:案例JoinType.Inner:#region 内部//获取行数据//要使用 DataTable.AsEnumerable() 扩展方法，您需要在项目中添加对 System.Data.DataSetExtension 程序集的引用.var rowDataLeftInner = from rowLeft in dtblLeft.AsEnumerable()在 rowLeft[colToJoinOn] 上的 dtblRight.AsEnumerable() 中加入 rowRight 等于 rowRight[strTempColName]选择 rowLeft.ItemArray.Concat(rowRight.ItemArray).ToArray();//添加行数据到dtblResultforeach(rowDataLeftInner 中的对象 [] 值)dtblResult.Rows.Add(values);#endregion休息;案例JoinType.Left:#region 左var rowDataLeftOuter = from rowLeft in dtblLeft.AsEnumerable()在 rowLeft[colToJoinOn] 上的 dtblRight.AsEnumerable() 中加入 rowRight 等于 rowRight[strTempColName] 到 gj来自 gj.DefaultIfEmpty() 中的 subRight选择 rowLeft.ItemArray.Concat((subRight== null) ? (dtblRight.NewRow().ItemArray) :subRight.ItemArray).ToArray();//添加行数据到dtblResultforeach(rowDataLeftOuter 中的对象 [] 值)dtblResult.Rows.Add(values);#endregion休息;}//将列名改回原来的dtblRight.Columns[strTempColName].ColumnName = colToJoinOn;//从结果中删除多余的列dtblResult.Columns.Remove(strTempColName);返回 dtblResult;}} 编辑 3:
此方法现在可以正常工作，并且当表有 2000 多行时仍然很快.任何建议/建议/改进将不胜感激.
编辑 4:
我有一个特定的场景，让我意识到以前的版本实际上是在进行内部联接.该功能已被修改以解决该问题.我使用了这个 link 上的信息来弄清楚.>
How can I Left Outer Join two data tables with the following tables and conditions while keeping all columns from both tables?
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
Conditions:
- In dtblLeft, col1 is not required to have unique values.
- In dtblRight, col1 has unique values.
- If dtblLeft is missing a foreign key in col1 or it has one that does not exist in dtblRight then empty or null fields will be inserted.
- Joining on col1.
I can use regular DataTable operations, LINQ, or whatever.
I tried this but it removes duplicates:
dtblA.PrimaryKey = new DataColumn[] {dtblA.Columns["col1"]}
DataTable dtblJoined = new DataTable();
dtblJoined.Merge(dtblA, false, MissingSchemaAction.AddWithKey);
dtblJoined.Merge(dtblB, false, MissingSchemaAction.AddWithKey);
EDIT 1:
This is close to I what I want but it only has columns from one of the tables ( found at this link ):
dtblJoined = (from t1 in dtblA.Rows.Cast<DataRow>()
join t2 in dtblB.Rows.Cast<DataRow>() on t1["col1"] equals t2["col1"]
select t1).CopyToDataTable();
EDIT 2:
An answer from this link seems to work for me but I had to change it a bit as follows:
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);
I also found this link and I might try that out since it seems more concise.
EDIT 3 (11/18/2013):
Updated tables to reflect more situations.
解决方案
Thanks all for your help. Here is what I came up with based on multiple resources:
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;
}
}
EDIT 3:
This method now works correctly and it is still fast when the tables have 2000+ rows. Any recommendations/suggestions/improvements would be appreciated.
EDIT 4:
I had a certain scenario that led me to realize the previous version was really doing an inner join. The function has been modified to fix that problem. I used info at this link to figure it out.
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