vb.net 使用 vb 2012 从 mysql 获取特定的行列值
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Get specific row col values from mysql using vb 2012
提问by Jay Wise
I have one button retrieve I just want to get the database table "account" value by its row and col and display it in a textbox. I keep on getting errors on the datafill line
我有一个按钮检索我只想通过其行和列获取数据库表“帐户”值并将其显示在文本框中。我一直在数据填充线上出错
Imports MySql.Data.MySqlClient
Public Class Form1
Dim dataset As DataSet
Dim datatable As DataTable
Dim sqlcon As MySqlConnection
Dim dataadapter As MySqlDataAdapter
Dim sqlcommand As MySqlCommand
Dim sql As String
Private Sub retrieve_Click(sender As Object, e As EventArgs) Handles retrieve.Click
sqlcon = New MySqlConnection("Data Source=localhost;Database=database;User ID=root;Password=;")
sqlcon.Open()
sql = "select * from account"
dataadapter = New MySqlDataAdapter(sql, sqlcon)
dataadapter.Fill(dataset)
TextBox2.Text = dataset.Tables(0).Rows(0).Item(0).ToString()
End Sub
End Class
回答by Steve
You need to instantiate the dataset that you pass to the Fill method.
您需要实例化传递给 Fill 方法的数据集。
....
dataset = new DataSet()
dataadapter.Fill(dataset)
...
Do not forget to close the connection when finished. It is a resource very costly to keep open when you not need it
完成后不要忘记关闭连接。在不需要时保持开放是一种成本非常高的资源
Using sqlcon = New MySqlConnection("Data Source=localhost;Database=database;User ID=root;Password=;")
sqlcon.Open()
sql = "select * from account"
dataadapter = New MySqlDataAdapter(sql, sqlcon)
dataset = new DataSet()
dataadapter.Fill(dataset)
TextBox2.Text = dataset.Tables(0).Rows(0).Item(0).ToString()
End Using
However if you need only one row it is better to refine the query applying a WHERE clause to limit the results returned by the database.
但是，如果您只需要一行，最好应用 WHERE 子句来优化查询以限制数据库返回的结果。
sql = "select * from account WHERE AccountName = @name"
dataadapter = New MySqlDataAdapter(sql, sqlcon)
dataadapter.SelectCommand.Parameters.AddWWithValue("@name", inputNameBox.Text)
dataset = new DataSet()
dataadapter.Fill(dataset, "Account")
if dataset.Tables("Account").Rows.Count > 0 then
TextBox2.Text = dataset.Tables("Account").Rows(0).Item(0).ToString()
End If
this hopefully will return just the row needed
这有望只返回所需的行
