从 SQL 查询返回多个变量

Question

我的表结构如下：

Session
--------------
SessionID (PK)
RoomID     
SessionDate
SessionTimeStart
SessionTimeEnd

我有一个以下查询，它将始终返回一行并显示在 DGV 中。我使用 DataAdapter 进行连接：

        DataTable queryResult = new DataTable();
        string ConnStr = "Data Source=DUZY;Initial Catalog=AutoRegSQL;Integrated Security=True";

        SqlConnection MyConn = new SqlConnection(ConnStr);
        MyConn.Open();

        //SQL query that returns todays sessions for the given roomID
        string query = @"SELECT SessionID, RoomID, SessionDate, SessionTimeStart, SessionTimeEnd" +
           " FROM [Session] " +
           " WHERE RoomID = @RoomID " +
           " AND SessionDate = cast(getdate() as date) ";

        SqlCommand command = new SqlCommand(query, MyConn);

        command.Parameters.Add("RoomID", SqlDbType.Char).Value = RoomID;


        SqlDataAdapter adapter = new SqlDataAdapter(command);

        adapter.Fill(queryResult);

我想将查询结果保存到表示表格列的多个字符串中，即

SessionIDstring = query result for SessionID column
RoomIDstring = query result for RoomID column
and so on...

是否可以使用一个查询来实现，还是我必须为每列创建 5 个查询？

Answer 1

类似的东西，也许，使用 ADO.NET？

    //SQL query that returns todays sessions for the given roomID
string query = @"SELECT SessionID, RoomID, SessionDate, SessionTimeStart, SessionTimeEnd" +
                " FROM [Session] " +
                " WHERE RoomID = @RoomID " +
                " AND SessionDate = cast(getdate() as date) ";

using (var connection = new SqlConnection(ConnStr))
using (var command = new SqlCommand(query, connection))
{
    command.Parameters.Add("RoomID", SqlDbType.Char).Value = RoomID;

    try
    {
        connection.Open();

        using (SqlDataReader reader = command.ExecuteReader())
        {
            if (reader.Read())
            {
                // Note that reader[x] has the equivalent type to the type
                // of the returned column, converted using
                // http://msdn.microsoft.com/en-us/library/cc716729.aspx
                // .ToString() if the item isn't null is always ok
                string SessionIDstring = reader[0].ToString(); // it should be an int

                // reading it twice is ok
                int RoomID = (int)reader[1]; // it should be an int
                string RoomIDstring = reader[1].ToString(); // it should be an int

                if (reader.Read())
                {
                    throw new Exception("Too many rows");
                }
            }
            else 
            {
                throw new Exception("No rows");
            }
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

此代码改编自 MSDN ADO.NET Code Examples。我添加了一些usings 并将其设为单行。我什至不想知道为什么 MSDN 示例没有完整地使用 using。

请注意，SqlDataAdapter 用于恢复多行/大数据并将它们放在DataSet 中。您可以将它们用于单行数据，但如果您只想填充一些变量，则只需使用 SqlDataReader 会容易得多。

Answer 2

declare @col1 int
declare @col2 varchar(42)

select  @col1 = col1
,       @col2 = col2
,       ....

Answer 3

你可以像这样创建一个类...

public class SessionDto
{
    public string SessionID {get; set;}  
    public string RoomID {get; set;}     
    public string SessionDate {get; set;} 
    public string SessionTimeStart {get; set;} 
    public string SessionTimeEnd {get; set;} 
}

然后有一个方法来获取房间 ID 并构建您的会话对象

public SessionDto GetSessionData(int roomId)
{
    using (var cnn = new SqlConnection(ConnStr))
    {
        SessionDto sessionDto;

        string query = @"SELECT SessionID, RoomID, SessionDate, SessionTimeStart, SessionTimeEnd" +
       " FROM [Session] " +
       " WHERE RoomID = @RoomID " +
       " AND SessionDate = cast(getdate() as date) ";


        cnn.Open();
        using (var cmd = new SqlCommand(query,cnn))
        {
            cmd.Parameters.Add("@RoomID", SqlDbType.Char).Value = roomId;

            using (var rdr = cmd.ExecuteReader())
            {
                if (rdr.HasRows)
                {
                    while (rdr.Read())
                    {
                        sessionDto = new sessionDto{
                            SessionID = rdr.GetString(0),
                            RoomID = rdr.GetString(1),
                            SessionDate = rdr.GetString(2),
                            SessionTimeStart = rdr.GetString(3),
                            SessionTimeEnd = rdr.GetString(4)
                        };
                    }
                }
            }
        }
    }
    return sessionDto;
}

因为我现在无法访问 VS，所以很多都是手动输入的， 但你应该让它工作。

另外，我用过rdr.GetString()，GetType()还有其他方法。