如何通过内部联接将两个DataTable联接在一起

Question

So I have 2 datatables that I want to merge into 1 in the same way that one merges with an inner join in sql server.

One catch is that some of the field names are the same in both tables, but the values may be different (eg. pricing values). The tables both have a column 'ID' that have the same value and can be joined.

Answer 1

You can do this by, assuming table1 and table2 are your two datatables, and resultTable is the DataTable you wish to populate with the results of the join. Also you can use union all operator.

Answer 2

Write a SQL SELECT statement that references tables in both of the databases, using a JOIN , assign aliases to the tables in the query, and then qualify the column references with the alias.

And use appropriate expressions in the SELECT list to return the resultset you want to return.

To emulate a "full outer" join, you may need to use a query with a LEFT JOIN , and another query with an ant-join, and combine the results with a UNION ALL operator.

Once you have a SELECT that returns the results you want, you can use that in an INSERT .. SELECT statement to save the results to another table.

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That's about as specific as we can be, without more specific information, beyond a vague description of what you are trying to achieve.

Answer 3

 DataTable dt1 = new DataTable();
    dt1.Columns.Add("CustID", typeof(int));
    dt1.Columns.Add("ColX", typeof(int));
    dt1.Columns.Add("ColY", typeof(int));

    DataTable dt2 = new DataTable();
    dt2.Columns.Add("CustID", typeof(int));
    dt2.Columns.Add("ColZ", typeof(int));

    for (int i = 1; i <= 5; i++)
    {
        DataRow row = dt1.NewRow();
        row["CustID"] = i;
        row["ColX"] = 10 + i;
        row["ColY"] = 20 + i;
        dt1.Rows.Add(row);

        row = dt2.NewRow();
        row["CustID"] = i;
        row["ColZ"] = 30 + i;
        dt2.Rows.Add(row);
    }

    var results = from table1 in dt1.AsEnumerable()
                 join table2 in dt2.AsEnumerable() on (int)table1["CustID"] equals (int)table2["CustID"]
                 select new
                 {
                     CustID = (int)table1["CustID"],
                     ColX = (int)table1["ColX"],
                     ColY = (int)table1["ColY"],
                     ColZ = (int)table2["ColZ"]
                 };
    foreach (var item in results)
    {
        Console.WriteLine(String.Format("ID = {0}, ColX = {1}, ColY = {2}, ColZ = {3}", item.CustID, item.ColX, item.ColY, item.ColZ));
    }
    Console.ReadLine();

// Output:
// ID = 1, ColX = 11, ColY = 21, ColZ = 31
// ID = 2, ColX = 12, ColY = 22, ColZ = 32
// ID = 3, ColX = 13, ColY = 23, ColZ = 33
// ID = 4, ColX = 14, ColY = 24, ColZ = 34
// ID = 5, ColX = 15, ColY = 25, ColZ = 35

Answer 4

Write a SQL SELECT statement that references tables in both of the databases, using a JOIN, assign aliases to the tables in the query, and then qualify the column references with the alias.

And use appropriate expressions in the SELECT list to return the resultset you want to return.

Answer 5

You should be able to do this, assuming table1 and table2 are your two datatables, and resultTable is the DataTable you wish to populate with the results of the join:

var res = from dr1 in table1.AsEnumerable()
            join dr2 in table2.AsEnumerable()
              on dr1.Field<int>("ID") equals dr2.Field<int>("ID")
          select resultTable.LoadDataRow(new object[]
          {
            dr1.Field<int>("ID"),
            dr1.Field<string>("column name .. "),
            ... 
            dr2.Field<string>("column from table 2 .. "),
            ...
           }, false);

and resultTable will then be populated with the rows with the fields you've chosen in the select.