Question

我正在尝试在vb.net中开发一个功能，以便在过期时自动标记mysql数据库中的项目，少于7天，不到一个月，少于2个月，少于3个月< / em>的。

我知道我使用的循环是正确的，基于右上方标签中的文字。但是，它只更新数据库中的一行。这是我得到的image。 所以问题是：我如何编码以便更新数据库中的所有行？

Public Sub insertStatus() Dim tDate As Date Dim eDate As Date Dim reader As MySqlDataReader Dim query, query2, updateQ1, updateQ2, updateQ3, updateQ4, updateQ5, updateQ6 As String Dim adpt As New MySqlDataAdapter Dim dSet As New DataSet Dim dRow As DataRow connection = New MySqlConnection connection.ConnectionString = "server=localhost;userid=luce;password=root;database=chemicalinventoryrecord;Allow Zero Datetime = True" Try connection.Open() tDate = Date.Today query = "select * from chemicalinventory" query2 = "select expiryDate from chemicalinventory" command = New MySqlCommand(query, connection) command1 = New MySqlCommand(query2, connection) adpt.SelectCommand = command adpt.Fill(dSet, "chemicalinventory") reader = command1.ExecuteReader While reader.Read For Each dRow In dSet.Tables(0).Rows eDate = CType(reader.GetMySqlDateTime("expiryDate"), Date) If (eDate - tDate).Days < 7 And (eDate - tDate).Days >= 1 Then lblTest2.Text = "Less than 7 days" updateQ1 = "update chemicalinventoryrecord.chemicalinventory set remark ='" & lblTest2.Text & "' where DateDiff(expiryDate, CURDATE())<7 and DateDiff(expiryDate, CURDATE())>=1 " command = New MySqlCommand(updateQ1, connection) Exit For ElseIf (tDate - eDate).Days >= 0 Then lblTest1.Text = "Expired" updateQ2 = "update chemicalinventoryrecord.chemicalinventory set remark = '" & lblTest1.Text & "' where DateDiff(CURDATE(), expiryDate)>=0" command2 = New MySqlCommand(updateQ2, connection) Exit For ElseIf (eDate - tDate).Days < 30 And (eDate - tDate).Days >= 7 Then updateQ3 = "update chemicalinventoryrecord.chemicalinventory set remark = 'Expiring in less than 1 month' where DateDiff(expiryDate, CURDATE())<30 and DateDiff(expiryDate, CURDATE())>=7" command4 = New MySqlCommand(updateQ3, connection) Exit For ElseIf (eDate - tDate).Days < 60 And (eDate - tDate).Days >= 30 Then lblTest3.Text = "Less than 2 month" updateQ4 = "update chemicalinventoryrecord.chemicalinventory set remark = '" & lblTest3.Text & "'where DateDiff(expiryDate, CURDATE())<60 and DateDiff(expiryDate, CURDATE())>=30" command5 = New MySqlCommand(updateQ4, connection) Exit For ElseIf (eDate - tDate).Days < 90 And (eDate - tDate).Days >= 60 Then updateQ5 = "update chemicalinventoryrecord.chemicalinventory set remark = 'Expiring in less than 3 months' where DateDiff(expiryDate, CURDATE())<90 and DateDiff(expiryDate, CURDATE())>=60" command6 = New MySqlCommand(updateQ5, connection) Exit For Else updateQ6 = "update chemicalinventoryrecord.chemicalinventory set remark =' ' where DateDiff(expiryDate, CURDATE())>90" command3 = New MySqlCommand(updateQ6, connection) Exit For End If Next End While reader.Close() command.ExecuteNonQuery() connection.Close() Catch ex As Exception MessageBox.Show(ex.Message) Finally connection.Dispose() End Try End Sub`

Answer 1

使用简单的存储过程从数据库中获取数据

Vb方面：

    Dim conn As New MySql.Data.MySqlClient.MySqlConnection
    Dim cmd As MySqlCommand = conn.CreateCommand()
    Dim myConnectionString As String
    Dim ds As New DataSet

    myConnectionString = "server=127.0.0.1;" _
                & "uid=Monica;" _
                & "pwd=12345;" _
                & "database=Monica;"

    Try
        conn.ConnectionString = myConnectionString
        conn.Open()  '' open connection

        If conn.State = ConnectionState.Open Then  '' check connection state 
            cmd.CommandText = "selectDataWithRemark"
            cmd.CommandType = CommandType.StoredProcedure
            Dim adap As MySqlDataAdapter = New MySqlDataAdapter(cmd)
            adap.Fill(ds)

        End If

        Try
            If Not ds Is Nothing Then  '' check ds before assigning to datagridview 

                If ds.Tables.Count > 0 Then
                    If ds.Tables(0).Rows.Count > 0 Then
                        dgvChemicalTable.DataSource = ds.Tables(0)
                    End If
                End If
            End If
        Catch ex As Exception
            MessageBox.Show("DataGridView Error : " & ex.Message)
        End Try

        conn.Close() '' close connection 


    Catch ex As MySql.Data.MySqlClient.MySqlException
        MessageBox.Show("Database Coonection Error : " & ex.Message)
    End Try

MySql方面：

       CREATE PROCEDURE `Monica`.`selectDataWithRemark` ()
       BEGIN


       SELECT Serial as Serial_Number,Name as Chemical_Name, 
              MolecularFormula  as Formula, DateReceived as Received_Date,
              DateExpired as Expiry_Date,
              DATEDIFF(DateExpired, DateReceived)     as Days_left,
              CASE
                 WHEN DATEDIFF(DateExpired, DateReceived) <= 0 THEN 'Expired'
                 WHEN DATEDIFF(DateExpired, DateReceived) < 7 THEN 'Expiring in less Less than 7 days'
                 WHEN DATEDIFF(DateExpired, DateReceived) < 30 THEN 'Expiring in less than 1 month'
                 WHEN DATEDIFF(DateExpired, DateReceived) < 60 THEN 'Expiring in less than 2 months'
                 WHEN DATEDIFF(DateExpired, DateReceived) < 90 THEN 'Expiring in less than 3 months'
                 ELSE 'Plenty of days left'
              END AS Remark

     FROM  test;

    END $$

----输出-----

PC @Tomalak使用了您的代码，但添加了else条件来处理null异常

Answer 2

创建一个列，其内容不是基于另一个列的值以外的其他因素，这是一个非常糟糕的主意。别这么做。

你想要的是这样的数据库查询：

SELECT
    col1, col2, etc, expiryDate,
    CASE
        WHEN DateDiff(CURDATE(), expiryDate) < 0 THEN 'Expired'
        WHEN DateDiff(CURDATE(), expiryDate) < 7 THEN 'Expiring in less Less than 7 days'
        WHEN DateDiff(CURDATE(), expiryDate) < 30 THEN 'Expiring in less than 1 month'
        WHEN DateDiff(CURDATE(), expiryDate) < 60 THEN 'Expiring in less than 2 months'
        WHEN DateDiff(CURDATE(), expiryDate) < 90 THEN 'Expiring in less than 3 months'
    END AS remark
FROM
    chemicalinventoryrecord.chemicalinventory

您可以将其存储为数据库视图，也可以直接在应用程序中使用它。

这样remark列始终是正确的，您不会需要每天运行的任何外部代码来保持最新状态。

从MySQL 5.7.5开始，如果您不想使用单独的视图，您甚至可以将CASE表达式添加为原始表格中的calculated column。

仅Foreach循环更新一个数据库行

2 个答案: