Question

我创建了一个返回表的SQL查询：

家庭|问题
一家人| 11
家庭b | 5
家庭c | 17个
家庭d | 28个

我在Visual Basic（visual studio 2015）中使用此代码将此数据返回到数据表：

using System;
using System.Data.OleDb;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Security.Cryptography;


namespace login
{
    public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    OleDbConnection con = new OleDbConnection();
    string dbprovider;
    string dbsource;
    DataSet ds = new DataSet();
    string username = "";
    string password = "";



    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        username = textBox1.Text;

    }

    private void textBox2_TextChanged(object sender, EventArgs e)
    {

    }



    private void Form1_Load(object sender, EventArgs e)
    {
        tabControl1.TabPages.Remove(tabPage2);
        // TODO: This line of code loads data into the 'login_data1DataSet.Table1' table. You can move, or remove it, as needed.
        this.table1TableAdapter.Fill(this.login_data1DataSet.Table1);

    }

    private void button1_Click(object sender, EventArgs e)
    {
        dbprovider  = "Provider=Microsoft.ACE.OLEDB.12.0;"; //If you’re an avid fan of Google you’ll see this line written in a number of different ways, version 12(this one) is suitable for our version of access.

        dbsource = "Data Source = ../login data1.accdb"; //Change this for the location and name of your db.

        con.ConnectionString = dbprovider + dbsource;

        con.Open(); //If you get this far you’re db is now opened successfully.
        OleDbCommand command = new OleDbCommand("SELECT username FROM table1 WHERE username = @username", con);
        command.Parameters.AddWithValue("@username", textBox1.Text);
        OleDbDataReader reader = command.ExecuteReader();
        if (!reader.HasRows)
        {
            MessageBox.Show("your username was not right");
            reader.Close();
            command.Dispose();
        }
        else
        {
            username = textBox1.Text;
            reader.Close();
            OleDbCommand command2 = new OleDbCommand("SELECT password FROM table1 WHERE password = @password", con);
            command2.Parameters.AddWithValue("@password", textBox2.Text);
            command2.Parameters.AddWithValue("@username", textBox1.Text);

            OleDbDataReader reader2 = command2.ExecuteReader();


            if (!reader2.HasRows)
            {
                // if (reader2.ToString != textBox2.Text)

                MessageBox.Show("your password was not right");
            }
            else
            {
                MessageBox.Show("logged in");
                tabControl1.TabPages.Insert(1,tabPage2);
                password = textBox2.Text;
            }


            reader2.Close();
            command2.Dispose();
           }
            con.Close();

    }
    }
}

*这里是我丢失的地方*

我需要代码根据第1列（家庭）中的值选择问题数量（第2列）

我的问题是，有些时候，其中一个家庭可能没有记录，所以数据集可能只有家庭a，c和d ......下次它可能有家庭b和d。所以我不能真正使用行（＃）。我需要能够引用姓氏的代码，然后返回问题的数量，将该数字放入字符串中，然后将该值放在文本框中。

我很高兴将字符串分配给变量然后进入文本框......它介于我之间，我无法弄明白！

谢谢！

Answer 1

我建议使用SqlDataAdapter来填充DataTable，然后使用Linq-To-DataTable来获取所需内容。另外，请始终使用using - 声明：

Dim table = New DataTable()
Using conn As New SqlConnection("connection string here")
    Using da = New SqlDataAdapter("select ........ ", conn)
        da.Fill(table)
    End Using
End Using

Dim matchingFamily = From row In table.AsEnumerable()
                     Where row.Field(Of String)("Family") = "family a"
If matchingFamily.Any() Then
    Dim familyIssueCount As Int32 = matchingFamily.First().Field(Of Int32)("Issues")
    ' ... '
End If

如果多个行可能包含此族，则可能使用不同的方法，因为First将选择任意行。一种方法是使用For Each枚举它们或使用matchingFamily.Sum(Function(r) r.Field(Of Int32)("Issues"))对问题求和。

如果您不需要内存中的所有记录，您也可以使用...WHERE Family = @family仅从数据库中选择相关记录。

Answer 2

Private Sub GetFamilyIssues(ByVal FamilyName As String)
    Dim cn As New SqlConnection("connection string here")
    cn.Open()

    Dim sql As String = "select * from FamilyIssues where FAMILY = @Family"

    Dim cmd As New SqlCommand(sql, cn)
    cmd.Parameters.AddWithValue("@Family", FamilyName)

    Dim reader As SqlDataReader = cmd.ExecuteReader

    txtIssues.Text = ""
    If reader.HasRows Then
        txtIssues.Text = reader("ISSUES").ToString()
    End If

    cn.Close()
End Sub

VB - sql查询到阅读器或数据表然后到文本框

2 个答案: