mysql - 如何忽略某些查询并执行其余查询？

Question

我有 5 个数据库，其中一些结构相同，有些则不同，例如 tbl_employee_debitcredit 该表不在其他数据库中，我想忽略不在数据库中的查询表并让其他查询执行。那可能吗？如果是的话怎么办？引用就够了。谢谢

已编辑:这是 for 循环和查询，如果缺少 1 个表，它将停止整个查询并继续到另一个数据库

Dim y As Integer = 0
For x = 0 To Form1.UcAddClient1.lv_acc.Items.Count + 1
    Dim a As Integer = 0

    Dim constr As String = "Server=" & Form1.UcAddClient1.lv_acc.Items(x).SubItems(y + 3).Text & "Database=" & Form1.UcAddClient1.lv_acc.Items(x).SubItems(y + 4).Text & ";User id=" & Form1.UcAddClient1.lv_acc.Items(x).SubItems(y + 5).Text & ";password=" & Form1.UcAddClient1.lv_acc.Items(x).SubItems(y + 6).Text & ";Convert Zero Datetime=True;"
    'MessageBox.Show(constr)

    Dim conn As New MySqlConnection(constr)

    Try
        If conn.State = ConnectionState.Closed Then
            conn.Open()
        End If

        Dim sqlcmd1 As New MySqlCommand("Select * from " &
            "(SELECT count(id) as Dept from departments where is_deleted = 0) as Dept, " &
            "(SELECT count(payroll_group_id) as pg from payroll_groups where is_deleted = 0) as pg , " &
            "(SELECT count(payroll_group_rate_id) as pgr from payroll_group_rates) as pgr, " &
            "(SELECT count(id) as leaves from leaves where is_deleted = 0) as leaves, " &
            "(SELECT count(id) as deminimis from de_minimis_benefits where is_deleted = 0 )as deminimis, " &
            "(SELECT employee_id from tbl_employee_debitcredit where is_deleted = 0 like '%1') and is_deleted = 0) as noODC ", conn)

        Dim dr1 As MySqlDataReader

        dr1 = sqlcmd1.ExecuteReader

        If dr1.HasRows Then
            While dr1.Read
                Dim newitem As New ListViewItem()

                newitem.Text = Form1.UcAddClient1.lv_acc.Items(x).SubItems(y + 1).Text.ToString
                newitem.SubItems.Add(Form1.UcAddClient1.lv_acc.Items(x).SubItems(y + 2).Text.ToString)
                newitem.SubItems.Add(dr1.Item("Dept").ToString)
                newitem.SubItems.Add(dr1.Item("pg").ToString)
                newitem.SubItems.Add(dr1.Item("pgr").ToString)
                newitem.SubItems.Add(dr1.Item("leaves").ToString)
                newitem.SubItems.Add(dr1.Item("deminimis").ToString)
                newitem.SubItems.Add(dr1.Item("noODC").ToString)
                lv_client_tracker.Items.Add(newitem)

            End While

            dr1.Close()

        End If

    Catch ex As Exception
        MessageBox.Show(ex.Message)

    End Try

    End If

Next

Answer 1

您需要查明该表是否存在于相应的环境中。我不知道mysql中的确切语法，但应该不难找到，我只是创建了一个空函数来模拟它。然后附加相应的查询，要么是真实的查询，要么是虚拟的查询，返回 0(或 -1 或您喜欢的任何内容)。

Private Sub Foo()
    Dim myExistsDepartments As Boolean = TableExists("departments", conn)
    Dim myExistsPayrollGroups As Boolean = TableExists("payroll_groups", conn)
    Dim myExistsPayrollGroupRates As Boolean = TableExists("payroll_group_rates", conn)
    Dim myExistsLeaves As Boolean = TableExists("leaves", conn)
    Dim myExistsDeMinimisBenefits As Boolean = TableExists("de_minimis_benefits", conn)
    Dim myExistsTblEmployeeDebitCredit As Boolean = TableExists("tbl_employee_debitcredit", conn)

    Dim myCommand As New StringBuilder("SELECT * FROM ")
    If (myExistsDepartments) Then
        myCommand.Append("(SELECT COUNT(id) FROM departments WHERE is_deleted = 0) AS Dept, ")
    Else
        myCommand.Append("0 AS Dept, ")
    End If
    If (myExistsPayrollGroups) Then
        myCommand.Append("(SELECT COUNT(payroll_group_id) FROM payroll_groups WHERE is_deleted = 0) AS pg, ")
    Else
        myCommand.Append("0 AS pg, ")
    End If
    If (myExistsPayrollGroupRates) Then
        myCommand.Append("(SELECT COUNT(payroll_group_rate_id) FROM payroll_group_rates) AS pgr, ")
    Else
        myCommand.Append("0 AS pgr, ")
    End If
    If (myExistsLeaves) Then
        myCommand.Append("(SELECT count(id) FROM leaves WHERE is_deleted = 0) AS leaves, ")
    Else
        myCommand.Append("0 AS leaves, ")
    End If
    If (myExistsDeMinimisBenefits) Then
        myCommand.Append("(SELECT count(id) FROM de_minimis_benefits WHERE is_deleted = 0) AS deminimis, ")
    Else
        myCommand.Append("0 AS deminimis, ")
    End If
    If (myExistsTblEmployeeDebitCredit) Then
        myCommand.Append("(SELECT employee_id FROM tbl_employee_debitcredit where is_deleted = 0) AS noODC ")
        'Or however this query should read correctly...
    Else
        myCommand.Append("0 AS noODC ")
    End If
    Dim sqlcmd1 As New MySqlCommand(myCommand.ToString(), conn)


End Sub

Private Function TableExists(tableName As String, conn As MySqlConnection) As Boolean
    'Put code here...
    Return True
End Function