Select from multiple tables in one call

问题:

In my code I have a page that includes information from 3 different tables. To show this information I make 3 SQL select calls and unite them in one list to pass as Model to my view. Can I do it with one SQL call? Data has no connection with one another.

My code:

public ActionResult Index()
{
    StorePageData PageData = new StorePageData();
    return View(PageData);
}
public class StorePageData
{
     public List<Table1Data> Table1 { get; set; }
     public List<Table2Data> Table2 { get; set; }
     public List<Table3Data> Table3 { get; set; }

     public StorePageData()
     {
          Table1  = //loading from Database1
          Table2  = //loading from Database2
          Table3  = //loading from Database3
     }
}
public class Table1Data
{
     public int Id { get; set; }
     public double Info1 { get; set; }
     public string Info2 { get; set; }
}
public class Table2Data
{
     public int Id { get; set; }
     public List<int> Info1 { get; set; }
     public List<int> Info2 { get; set; }
}
public class Table3Data
{
     public int Id { get; set; }
     public List<string> Info1 { get; set; }
     public List<string> Info2 { get; set; }
}

If there is a way to load all 3 tables in one SQL request it will improve significantly the load time of this page.

Thank you.

回答1:

You can get multiple result sets in a single request using a DataReader. You can use it with or without entity framework.

If you are using Entity Framework, you can pass a DbDataReader to ObjectContext.Translate method to translate multiple result set to requested object types. The command which is used to create the data reader can be a stored procedure, or you can simply use a command containing your queries to shape multiple result set.

Example

List<Table1> list1;
List<Table2> list2;

using (var cn = new SqlConnection(@"Connection String"))
{
    cn.Open();
    using (var cmd = cn.CreateCommand())
    {
        cmd.CommandText = "SELECT * FROM Table1; SELECT * FROM Table2";
        var reader = cmd.ExecuteReader(); 
        using (var db = new YourDbContext())
        {
            var context = ((IObjectContextAdapter)db).ObjectContext;
            list1 = context.Translate<Table1>(reader).ToList();
            reader.NextResult();
            list2 = context.Translate<Table2>(reader).ToList();
        }
    }
}

If you are using SqlDataAdapter, you can simply pass a command containing your queries and then using Fill, fill a data set. The data adapter itself will use DataReader behind the scene.

Example

var connectionString = @"Connection String";
var commandText = "SELECT * FROM Table1; SELECT * FROM Table2;";
var ds = new DataSet();
using (var da = new SqlDataAdapter(commandText, connectionString))
{
    da.Fill(ds);
}

Then you can shape the results to List<Table1> and List<Table2>.

回答2:

DO NOT USE UNION. DataAdapter is weapon of choise.

var commandText = "SELECT * FROM Table1; SELECT * FROM Table2;";
var ds = new DataSet();
using (var da = new SqlDataAdapter(commandText, "your cn"))
{
    da.Fill(ds);
}

Using:

ds.Tables["Table1"]...
ds.Tables["Table2"]...

回答3:

You can use UNION ALL to merge multiple queries.

Do something like this:

SELECT * FROM Table1
UNION ALL
SELECT * FROM Table2

Edit:

You can do this if you want to know where a single record is from:

SELECT *, 1 AS TableName FROM Table1
UNION ALL
SELECT *, 2 AS TableName FROM Table2

This will add another column that can be used to split the array into 3 lists.

回答4:

Assuming you are using EntityFramwork you can use EF Stored procedure that returns multiple result sets. Then map the result tables to your class object. Take a look here or google it. It will take one round to the DB.

回答5:

You can do something like this

SELECT  Info1, Info2 
FROM Table1Data
UNION ALL
SELECT Id, Info2 
FROM Table2Data;

Then you can parse the result. Depends on the case but you can also consider using a transaction.

回答6:

May be this can helpful to you.

Select the three tables in a single procedure as a separate result sets, and then in the C# side get the result sets and convert it into JSON format, and then from the JSON you can get the each table data into your list.

DataSet dataSet = new DataSet("dataSet");
dataSet.Namespace = "NetFrameWork";
DataTable table = new DataTable();
DataColumn idColumn = new DataColumn("id", typeof(int));
idColumn.AutoIncrement = true;

DataColumn itemColumn = new DataColumn("item");
table.Columns.Add(idColumn);
table.Columns.Add(itemColumn);
dataSet.Tables.Add(table);

for (int i = 0; i < 2; i++)
{
    DataRow newRow = table.NewRow();
    newRow["item"] = "item " + i;
    table.Rows.Add(newRow);
}

dataSet.AcceptChanges();

string json = JsonConvert.SerializeObject(dataSet, Formatting.Indented);

Console.WriteLine(json);


//{
     // "Table1": [
     //   {
      //    "id": 0,
     //     "item": "item 0"
     //   },
     //   {
     //    "id": 1,
     //     "item": "item 1"
     //   }
     //  ]
    //"Table2": [
      //  {
       //   "id": 0,
       //   "item": "item 0",
         // "rate": 200.00
       // },
       // {
        // "id": 1,
        //  "item": "item 1",
        //   "rate": 225.00
        //}
      // ]

   // "Table3": [
       // {
       //   "id": 0,
       //   "item": "item 0",
       //   "rate": 200.00,
       //   "UOM" : "KG"
       // },
       // {
       //  "id": 1,
       //   "item": "item 1",
       //    "rate": 225.00,
       //   "UOM" : "LTR"
       // }
      // ]
     //}

回答7:

you can use below generic code snippet

      /// <method>

    /// Select Query

    /// </method>

    public DataTable executeSelectQuery(String _query, SqlParameter[] sqlParameter)

    {
        SqlCommand myCommand = new SqlCommand();

        DataTable dataTable = new DataTable();

        dataTable = null;

        DataSet ds = new DataSet();

        try

        {
            myCommand.Connection = openConnection();
            myCommand.CommandText = _query;//or proc
            myCommand.Parameters.AddRange(sqlParameter);
            myAdapter.SelectCommand = myCommand;
            myAdapter.Fill(ds);

            dataTable = ds.Tables[0];//as per your requirement
        }
        catch (SqlException e)

        {//any logger 
            Console.Write("Error - Connection.executeSelectQuery - Query: " + _query + " \nException: " + e.StackTrace.ToString());
            return null;

        }            
            return dataTable;
    }