Question

I need to merge two data schema into one. I have Schema1 and Schema2. I need to join these two into Schema3. Furthermore, I have a Select statement which queries a data set but I can’t figure out how to use the select statement on the data set containing both tables (both Schema1 and Schema2) and combine them into the new table schema3 which is a table in the same data set comprised of both table’s fields.

Example

Schema 1
ID,
Food,
Book,
Rice,
Cave

Schema 2
ID ,
Carpet,
Strings,
Run

Schema 3
ID,
Food,
Book,
Rice,
Cave,
Carpet,
Strings,
Run

Fill the Schema3 Table with this command

Sql Command:

Select * Schema1 [except ID] and all fields from Schema2 [exceptID] Inner Join 
Schema2 ON Schema1.ID = Schema2.ID
Where ID = {dynamically defined variable 'X'}

Please excuse the lack of proper syntax. The main issue here again is querying a dataset with the select statement and filling up a table with the results. Im not exactly connecting to my DB because I already filled a dataset locally.

——Edit ——
I really just need a way to create an array of data rows from a query of two tables.

Answer 1

You could use this extension method here which i’ve written from scratch recently for another question. It enables to merge multiple tables by a common key. If no key is specified it will just use the default DataTable.Merge method:

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[] { Schema1, Schema2};
DataTable Schema3 = tables.MergeAll("ID");

Edit: If you don’t need a new DataTable with the merged schema you could also use Linq-To-DataSet (now VB.NET):

Dim schema3 = From r1 In schema1
          Join r2 In schema2 On r1.Field(Of Int32)("ID") Equals r2.Field(Of Int32)("ID")
          Select New With {
                .ID = r1.Field(Of Int32)("ID"),
                .Food = r1.Field(Of String)("Food"),
                .Book = r1.Field(Of String)("Book"),
                .Rice = r1.Field(Of String)("Rice"),
                .Cave = r1.Field(Of String)("Cave"),
                .Carpet = r2.Field(Of String)("Carpet"),
                .Strings = r2.Field(Of String)("Strings"),
                .Run = r2.Field(Of String)("Run")
            }