Combining N Datatables into a Single Datatable

Combining n DataTables into a Single DataTable

The table has repeating primary keys after the Merge because no primary-key was defined. So either specify the PK or try this method here which i've written from scratch~~(so it's not really tested)~~:

public static DataTable MergeAll(this IList<DataTable> tables, String primaryKeyColumn)
{
    if (!tables.Any())
        throw new ArgumentException("Tables must not be empty", "tables");
    if(primaryKeyColumn != null)
        foreach(DataTable t in tables)
            if(!t.Columns.Contains(primaryKeyColumn))
                throw new ArgumentException("All tables must have the specified primarykey column " + primaryKeyColumn, "primaryKeyColumn");

    if(tables.Count == 1)
        return tables[0];

    DataTable table = new DataTable("TblUnion");
    table.BeginLoadData(); // Turns off notifications, index maintenance, and constraints while loading data
    foreach (DataTable t in tables)
    {
        table.Merge(t); // same as table.Merge(t, false, MissingSchemaAction.Add);
    }
    table.EndLoadData();

    if (primaryKeyColumn != null)
    {
        // since we might have no real primary keys defined, the rows now might have repeating fields
        // so now we're going to "join" these rows ...
        var pkGroups = table.AsEnumerable()
            .GroupBy(r => r[primaryKeyColumn]);
        var dupGroups = pkGroups.Where(g => g.Count() > 1);
        foreach (var grpDup in dupGroups)
        { 
            // use first row and modify it
            DataRow firstRow = grpDup.First();
            foreach (DataColumn c in table.Columns)
            {
                if (firstRow.IsNull(c))
                {
                    DataRow firstNotNullRow = grpDup.Skip(1).FirstOrDefault(r => !r.IsNull(c));
                    if (firstNotNullRow != null)
                        firstRow[c] = firstNotNullRow[c];
                }
            }
            // remove all but first row
            var rowsToRemove = grpDup.Skip(1);
            foreach(DataRow rowToRemove in rowsToRemove)
                table.Rows.Remove(rowToRemove);
        }
    }

    return table;
}

You can call it in this way:

var tables = new[] { tblA, tblB, tblC };
DataTable TblUnion = tables.MergeAll("c1");

Used this sample data:

var tblA = new DataTable();
tblA.Columns.Add("c1", typeof(int));
tblA.Columns.Add("c2", typeof(int));
tblA.Columns.Add("c3", typeof(string));
tblA.Columns.Add("c4", typeof(char));

var tblB = new DataTable();
tblB.Columns.Add("c1", typeof(int));
tblB.Columns.Add("c5", typeof(int));
tblB.Columns.Add("c6", typeof(string));
tblB.Columns.Add("c7", typeof(char));

var tblC = new DataTable();
tblC.Columns.Add("c1", typeof(int));
tblC.Columns.Add("c8", typeof(int));
tblC.Columns.Add("c9", typeof(string));
tblC.Columns.Add("c10", typeof(char));

tblA.Rows.Add(1, 8500, "abc", 'A');
tblA.Rows.Add(2, 950, "cde", 'B');
tblA.Rows.Add(3, 150, "efg", 'C');
tblA.Rows.Add(4, 850, "ghi", 'D');
tblA.Rows.Add(5, 50, "ijk", 'E');

tblB.Rows.Add(1, 7500, "klm", 'F');
tblB.Rows.Add(2, 900, "mno", 'G');
tblB.Rows.Add(3, 150, "opq", 'H');
tblB.Rows.Add(4, 850, "qrs", 'I');
tblB.Rows.Add(5, 50, "stu", 'J');

tblC.Rows.Add(1, 7500, "uvw", 'K');
tblC.Rows.Add(2, 900, "wxy", 'L');
tblC.Rows.Add(3, 150, "yza", 'M');
tblC.Rows.Add(4, 850, "ABC", 'N');
tblC.Rows.Add(5, 50, "CDE", 'O');

After DataTable.Merge in MergeAll:

Sample Image

After some modifications to join the rows in MergeAll:

Sample Image

Update

Since this question arose in one of the comments, if the only relation between two tables is the index of a DataRow in the table and you want to merge both tables according to the index:

public static DataTable MergeTablesByIndex(DataTable t1, DataTable t2)
{
    if (t1 == null || t2 == null) throw new ArgumentNullException("t1 or t2", "Both tables must not be null");

    DataTable t3 = t1.Clone();  // first add columns from table1
    foreach (DataColumn col in t2.Columns)
    {
        string newColumnName = col.ColumnName;
        int colNum = 1;
        while (t3.Columns.Contains(newColumnName))
        {
            newColumnName = string.Format("{0}_{1}", col.ColumnName, ++colNum);
        }
        t3.Columns.Add(newColumnName, col.DataType);
    }
    var mergedRows = t1.AsEnumerable().Zip(t2.AsEnumerable(),
        (r1, r2) => r1.ItemArray.Concat(r2.ItemArray).ToArray());
    foreach (object[] rowFields in mergedRows)
        t3.Rows.Add(rowFields);

    return t3;
}

Sample:

var dt1 = new DataTable();
dt1.Columns.Add("ID", typeof(int));
dt1.Columns.Add("Name", typeof(string));
dt1.Rows.Add(1, "Jon");
var dt2 = new DataTable();
dt2.Columns.Add("Country", typeof(string));
dt2.Rows.Add("US");

var dtMerged = MergeTablesByIndex(dt1, dt2);

The result table contains three columns ID,Name,Country and a single row: 1 Jon US

Combining two c# datatables into one

If your objective is just to merge data without considering the relationship between the two data then you can add two more columns into first datatable and through loop get data from second table and assign them to first datatable columns. The way the data is received will be the way data will be saved in first datatable.

public DataTable MergeData(DataTable dtFirst,DataTable dtSecond)
{
    dtFirst.Columns.Add("LocalAuthority");
    dtFirst.Columns.Add("AverageSpeed");
    for (int i = 0; i < dtFirst.Rows.Count; i++)
    {
        dtFirst.Rows[i]["LocalAuthority"] = dtSecond.Rows[i]["LocalAuthority"];
        dtFirst.Rows[i]["AverageSpeed"] = dtSecond.Rows[i]["AverageSpeed"];
    }
    return dtFirst;
}

Now , you need to pass datatable as parameter in following method.

MergeData(allTables.ElementAt(0), allTables.ElementAt(1));

Join two datatables different columnName into one datatable

If you mean join by index, it's more a zip of two DataTables. You could use this method:

public static DataTable MergeTablesByIndex(DataTable t1, DataTable t2)
{
    if (t1 == null || t2 == null) throw new ArgumentNullException("t1 or t2", "Both tables must not be null");

    DataTable t3 = t1.Clone();  // first add columns from table1
    foreach (DataColumn col in t2.Columns)
    {
        string newColumnName = col.ColumnName;
        int colNum = 1;
        while (t3.Columns.Contains(newColumnName))
        {
            newColumnName = string.Format("{0}_{1}", col.ColumnName, ++colNum);
        }
        t3.Columns.Add(newColumnName, col.DataType);
    }
    var mergedRows = t1.AsEnumerable().Zip(t2.AsEnumerable(),
        (r1, r2) => r1.ItemArray.Concat(r2.ItemArray).ToArray());
    foreach (object[] rowFields in mergedRows)
        t3.Rows.Add(rowFields);

    return t3;
}

I haven't written this from scratch, it's second part of an older answer of me.

How to merge multiple datatables (every datatable return one row) in one row

So empNum is the key column which all tables share? It sounds as if you could use my MergeAll:

public static DataTable MergeAll(this IList<DataTable> tables, String primaryKeyColumn)
{
    if (!tables.Any())
        throw new ArgumentException("Tables must not be empty", "tables");
    if(primaryKeyColumn != null)
        foreach(DataTable t in tables)
            if(!t.Columns.Contains(primaryKeyColumn))
                throw new ArgumentException("All tables must have the specified primarykey column " + primaryKeyColumn, "primaryKeyColumn");

    if(tables.Count == 1)
        return tables[0];

    DataTable table = new DataTable("TblUnion");
    table.BeginLoadData(); // Turns off notifications, index maintenance, and constraints while loading data
    foreach (DataTable t in tables)
    {
        foreach (DataColumn col in t.Columns) 
            col.ReadOnly = false; // this might be required in your case
        table.Merge(t); // same as table.Merge(t, false, MissingSchemaAction.Add);
    }
    table.EndLoadData();

    if (primaryKeyColumn != null)
    {
        // since we might have no real primary keys defined, the rows now might have repeating fields
        // so now we're going to "join" these rows ...
        var pkGroups = table.AsEnumerable()
            .GroupBy(r => r[primaryKeyColumn]);
        var dupGroups = pkGroups.Where(g => g.Count() > 1);
        foreach (var grpDup in dupGroups)
        { 
            // use first row and modify it
            DataRow firstRow = grpDup.First();
            foreach (DataColumn c in table.Columns)
            {
                if (firstRow.IsNull(c))
                {
                    DataRow firstNotNullRow = grpDup.Skip(1).FirstOrDefault(r => !r.IsNull(c));
                    if (firstNotNullRow != null)
                        firstRow[c] = firstNotNullRow[c];
                }
            }
            // remove all but first row
            var rowsToRemove = grpDup.Skip(1);
            foreach(DataRow rowToRemove in rowsToRemove)
                table.Rows.Remove(rowToRemove);
        }
    }

    return table;
}

Then use it in this way:

var tables = new[] { tblEmp_data, tblEmp_time, tbl_emp_mission };
tblEmp_data = tables.MergeAll("empNum");

Merge 2 DataTables and store in a new one

The Merge method takes the values from the second table and merges them in with the first table, so the first will now hold the values from both.

If you want to preserve both of the original tables, you could copy the original first, then merge:

dtAll = dtOne.Copy();
dtAll.Merge(dtTwo);

Combining N Datatables into a Single Datatable