特定のイベントで参加したユーザーを表示する

Question

私はイベント管理システムをVisual Studio 2013に作成したので、私たちのシステムにユニークな参加ユーザーを表示する方法を尋ねたいだけです。既に作成されたイベントコードを試しましたが、動作しません。エラーはありませんが、動作しません。手伝って頂けますか？前もって感謝します。ここで

は私のコードです：

private void tbx_joined_TextChanged(object sender, EventArgs e) 
    { 
     String Query = "select count(distinct d.jusername) from dbems.db_join d, dbems.create_event c where d.jeventname = c.eventname"; 
     MySqlConnection conDataBase = new MySqlConnection(db.mystring()); 
     MySqlCommand cmdDataBase = new MySqlCommand(Query, conDataBase); 
     MySqlDataReader myReader; 

     try 
     { 
      conDataBase.Open(); 
      myReader = cmdDataBase.ExecuteReader(); 

      while (myReader.Read()) 
      { 
       //"count(distinct d.jusername)" 
       string evjoined = myReader.GetInt32(Query).ToString(); 

       tbx_joined.Text = evjoined; 

      } 
     } 

     catch (Exception) 
     { 

     } 

    } 

Answer 1

ここでは、あなたのテーブルとデータを修正するために実行するスクリプトです：

--USE your db here 
USE [Breaz] 
GO 
/****** Object: Table [dbo].[dbemEvent] Script Date: 5/10/2017 4:01:15 PM ******/ 
SET ANSI_NULLS ON 
GO 
SET QUOTED_IDENTIFIER ON 
GO 
SET ANSI_PADDING ON 
GO 
CREATE TABLE [dbo].[dbemEvent](
    [Id] [int] IDENTITY(1,1) NOT NULL, 
    [EventName] [varchar](15) NOT NULL, 
CONSTRAINT [PK_dbemEvent] PRIMARY KEY CLUSTERED 
(
    [Id] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] 

GO 
SET ANSI_PADDING OFF 
GO 
/****** Object: Table [dbo].[dbemUser] Script Date: 5/10/2017 4:01:15 PM ******/ 
SET ANSI_NULLS ON 
GO 
SET QUOTED_IDENTIFIER ON 
GO 
SET ANSI_PADDING ON 
GO 
CREATE TABLE [dbo].[dbemUser](
    [Id] [int] IDENTITY(1,1) NOT NULL, 
    [Event] [int] NULL, 
    [UserName] [varchar](15) NULL, 
CONSTRAINT [PK_dbemUser] PRIMARY KEY CLUSTERED 
(
    [Id] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] 

GO 
SET ANSI_PADDING OFF 
GO 
SET IDENTITY_INSERT [dbo].[dbemEvent] ON 

GO 
INSERT [dbo].[dbemEvent] ([Id], [EventName]) VALUES (1, N'School') 
GO 
INSERT [dbo].[dbemEvent] ([Id], [EventName]) VALUES (2, N'Home') 
GO 
SET IDENTITY_INSERT [dbo].[dbemEvent] OFF 
GO 
SET IDENTITY_INSERT [dbo].[dbemUser] ON 

GO 
INSERT [dbo].[dbemUser] ([Id], [Event], [UserName]) VALUES (1, 1, N'Bob') 
GO 
INSERT [dbo].[dbemUser] ([Id], [Event], [UserName]) VALUES (2, 1, N'Ken') 
GO 
INSERT [dbo].[dbemUser] ([Id], [Event], [UserName]) VALUES (3, 2, N'Nick') 
GO 
INSERT [dbo].[dbemUser] ([Id], [Event], [UserName]) VALUES (4, 2, N'Jack') 
GO 
SET IDENTITY_INSERT [dbo].[dbemUser] OFF 
GO 
ALTER TABLE [dbo].[dbemUser] WITH CHECK ADD CONSTRAINT [FK_dbemUser_dbemEvent] FOREIGN KEY([Event]) 
REFERENCES [dbo].[dbemEvent] ([Id]) 
GO 
ALTER TABLE [dbo].[dbemUser] CHECK CONSTRAINT [FK_dbemUser_dbemEvent] 
GO 

ここではあなたが使用できる新しいクエリです：

SELECT COUNT(u.id) 
FROM dbemUser u JOIN 
dbemEvent e 
ON u.Event = e.Id 
WHERE e.EventName = 'Home'