Solved

C# Left join 2 DataTables without knowing the content of each, just the join key

Posted on 2014-01-21
5
1,112 Views
Last Modified: 2016-02-10
I have 2 C# DataTables that I want to left join in order to create a combined DataTable.
I know the name of the column that joins the table, but nothing else, as the use imports the 2 tables at startup. The joining column is 'UPC'

1. What is a code example to join the 2 tables together to a third DataTable with all columns?
2. If there are column with the same name in each table will it be a problem for the join? If so, is there any solution?
0
Comment
Question by:esak2000
  • 3
  • 2
5 Comments
 
LVL 44

Expert Comment

by:AndyAinscow
ID: 39797015
SELECT T1.*, T2.* FROM T1  left JOIN T2 ON T1.UPC = T2.UPC

where T1 and T2 are the table names you have
0
 
LVL 44

Expert Comment

by:AndyAinscow
ID: 39797019
>>If there are column with the same name in each table will it be a problem for the join?

NO, but you need to refer to them with the table names eg.
T1.x or T2.x  (so you know which field called x is coming from which table)
0
 

Author Comment

by:esak2000
ID: 39797113
that's a standard sql query, I need the LINQ equivalent for .net datatables
0
 

Accepted Solution

by:
esak2000 earned 0 total points
ID: 39902566
¿
the following code worked:


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace JoinDataTables
{
    public static class DataTableJoinHelper
    {
        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>       
        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;
        }
    }
}

Open in new window

0
 

Author Closing Comment

by:esak2000
ID: 39914413
This class worked as a solution worked to join the 2 datatables
0

Featured Post

3 Use Cases for Connected Systems

Our Dev teams are like yours. They’re continually cranking out code for new features/bugs fixes, testing, deploying, testing some more, responding to production monitoring events and more. It’s complex. So, we thought you’d like to see what’s working for us.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

PL/SQL can be a very powerful tool for working directly with database tables. Being able to loop will allow you to perform more complex operations, but can be a little tricky to write correctly. This article will provide examples of basic loops alon…
Occasionally there is a need to clean table columns, especially if you have inherited legacy data. There are obviously many ways to accomplish that, including elaborate UPDATE queries with anywhere from one to numerous REPLACE functions (even within…
This tutorial gives a high-level tour of the interface of Marketo (a marketing automation tool to help businesses track and engage prospective customers and drive them to purchase). You will see the main areas including Marketing Activities, Design …
This Micro Tutorial demonstrates using Microsoft Excel pivot tables, how to reverse engineer competitors' marketing strategies through backlinks.

773 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question