Mysql 检查表是否已存在，但它'；“s不工作接收错误”；值不能为null。参数名称：dataTable"；

检查表是否已经存在，但它不工作：接收错误“值不能为null。参数名称：dataTable”

这是密码

Sub TABLES_CHK()
    Try
        tbl_lbl.Text = "TABLES EXISTS: " & DoesTABLEExist("server=localhost; username=root; password=*****; database=*****;")
        If DoesTABLEExist("server=localhost; username=root; password=*****; database=*****;") = False Then
            Exit Sub
            Using CON As New MySqlConnection("server=localhost; username=*****; password=*****;  database=*******;")
                Using adapter As New MySqlDataAdapter("CREATE TABLE `airtech_db`.`employees`(" &
            "`Employee_ID` INT Not NULL AUTO_INCREMENT,`Name` VARCHAR(45) NULL,FATHER_NAME VARCHAR(45) NULL," &
            "DOB VARCHAR(45) NULL,DOJ VARCHAR(45) NULL,POSITION VARCHAR(45) NULL,EMP_STATUS VARCHAR(45) NULL," &
            "SALARY VARCHAR(45) NULL,EOS VARCHAR(45) NULL,REMARKS VARCHAR(45) NULL," &
            "PRIMARY KEY(`Employee_ID`))", CON)
                    CON.Open()
                    Dim dt As New DataTable
                    adapter.Fill(dt)
                    CON.Close()
                End Using
            End Using
        End If
        tbl_lbl.Text += " -TABLES CREATED: " & DoesDBExist("server=localhost; username=root; password=*****;")
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub
Function DoesTABLEExist(DBConnectionString As String) As Boolean
    Try
        Dim conn As MySqlConnection = New MySqlConnection(DBConnectionString)
        Dim ADAPTER As New MySqlDataAdapter("Select * From information_schema.tables" &
                                 " Where table_schema = 'airtech_db' And table_name = 'employees' LIMIT 1;", conn)
        Dim DT As DataTable, TABLECHK As Boolean

        conn.Open()
        ADAPTER.Fill(DT)
        MsgBox(DT.Rows.Count)
        If DT.Rows.Count > 0 Then
            TABLECHK = True
        Else
            TABLECHK = False
        End If
        conn.Close()
        Return TABLECHK
    Catch ex As Exception

            MsgBox(ex.Message)
        End If
    End Try
End Function

---

暂时删除

Try

，以便查看导致错误的行

公开

.Dispose

方法的数据库对象希望调用该方法，因为它们可能正在使用需要释放的非托管资源。这发生在他们的

.Dispose

方法中。即使出现错误，

Using…End Using

块也会为您处理此问题

无需创建

数据适配器

或

数据表

。不要从服务器中提取不需要的数据。你只需要数一数。使用

.ExecuteScalar

，将结果集第一行的第一列作为对象返回

Function DoesTABLEExist(DBConnectionString As String) As Boolean
    Dim RetVal As Integer
    Using conn As New MySqlConnection(DBConnectionString),
           cmd As New MySqlCommand("Select Count(*) From information_schema.tables
                                    Where table_schema = 'airtech_db' 
                                    And table_name = 'employees';", conn)
        conn.Open()
        RetVal = CInt(cmd.ExecuteScalar())
    End Using
    Dim TABLECHK As Boolean
    If RetVal > 0 Then
        TABLECHK = True
    Else
        TABLECHK = False
    End If
    Return TABLECHK
End Function

---

暂时删除

Try

，以便查看导致错误的行

公开

.Dispose

方法的数据库对象希望调用该方法，因为它们可能正在使用需要释放的非托管资源。这发生在他们的

.Dispose

方法中。即使出现错误，

Using…End Using

块也会为您处理此问题

无需创建

数据适配器

或

数据表

。不要从服务器中提取不需要的数据。你只需要数一数。使用

.ExecuteScalar

，将结果集第一行的第一列作为对象返回

Function DoesTABLEExist(DBConnectionString As String) As Boolean
    Dim RetVal As Integer
    Using conn As New MySqlConnection(DBConnectionString),
           cmd As New MySqlCommand("Select Count(*) From information_schema.tables
                                    Where table_schema = 'airtech_db' 
                                    And table_name = 'employees';", conn)
        conn.Open()
        RetVal = CInt(cmd.ExecuteScalar())
    End Using
    Dim TABLECHK As Boolean
    If RetVal > 0 Then
        TABLECHK = True
    Else
        TABLECHK = False
    End If
    Return TABLECHK
End Function

---

为了检查表是否已经存在，这段代码工作得很好

Sub TABLES_CHK()
    Dim CON_STRING As String
    CON_STRING = "server=localhost; username=root; password=****; database=****;"
    Try
        tbl_lbl.Text = "TABLES EXISTS: " & DoesTABLEExist(CON_STRING)
        If DoesTABLEExist(CON_STRING) = False Then
            Using CON As New MySqlConnection(CON_STRING)
                Using adapter As New MySqlDataAdapter("CREATE TABLE `airtech_db`.`employees`(" &
            "`Employee_ID` INT Not NULL AUTO_INCREMENT,`Name` VARCHAR(45) NULL,FATHER_NAME VARCHAR(45) NULL," &
            "DOB VARCHAR(45) NULL,DOJ VARCHAR(45) NULL,POSITION VARCHAR(45) NULL,EMP_STATUS VARCHAR(45) NULL," &
            "SALARY VARCHAR(45) NULL,EOS VARCHAR(45) NULL,REMARKS VARCHAR(45) NULL," &
            "PRIMARY KEY(`Employee_ID`))", CON)
                    CON.Open()
                    Dim dt As New DataTable
                    adapter.Fill(dt)
                    CON.Close()
                End Using
            End Using
            tbl_lbl.Text += " -TABLES CREATED: " & DoesDBExist(CON_STRING)
        Else
            tbl_lbl.Text += " -TABLES CREATED: False"
        End If

    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub
Function DoesTABLEExist(DBConnectionString As String) As Boolean

    Try
        Dim conn As MySqlConnection = New MySqlConnection(DBConnectionString)
        ' Dim ADAPTER As New MySqlDataAdapter("Select * From information_schema.tables" &
        '                         " Where table_schema = 'airtech_db' And table_name = 'employees' LIMIT 1;", conn)
        Dim cmd As New MySqlCommand("Select * From information_schema.tables Where table_schema = 'airtech_db' And table_name = 'employees' LIMIT 1;", conn)


        conn.Open()
        Dim bRet As Boolean = False
        Dim reader As MySqlDataReader = cmd.ExecuteReader
        bRet = reader.HasRows
        If (bRet = True) Then
            'MsgBox("Table Exists")
        Else
            ' MsgBox("No more records")
        End If
        conn.Close()
        Return bRet

    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Function

---

为了检查表是否已经存在，这段代码工作得很好

Sub TABLES_CHK()
    Dim CON_STRING As String
    CON_STRING = "server=localhost; username=root; password=****; database=****;"
    Try
        tbl_lbl.Text = "TABLES EXISTS: " & DoesTABLEExist(CON_STRING)
        If DoesTABLEExist(CON_STRING) = False Then
            Using CON As New MySqlConnection(CON_STRING)
                Using adapter As New MySqlDataAdapter("CREATE TABLE `airtech_db`.`employees`(" &
            "`Employee_ID` INT Not NULL AUTO_INCREMENT,`Name` VARCHAR(45) NULL,FATHER_NAME VARCHAR(45) NULL," &
            "DOB VARCHAR(45) NULL,DOJ VARCHAR(45) NULL,POSITION VARCHAR(45) NULL,EMP_STATUS VARCHAR(45) NULL," &
            "SALARY VARCHAR(45) NULL,EOS VARCHAR(45) NULL,REMARKS VARCHAR(45) NULL," &
            "PRIMARY KEY(`Employee_ID`))", CON)
                    CON.Open()
                    Dim dt As New DataTable
                    adapter.Fill(dt)
                    CON.Close()
                End Using
            End Using
            tbl_lbl.Text += " -TABLES CREATED: " & DoesDBExist(CON_STRING)
        Else
            tbl_lbl.Text += " -TABLES CREATED: False"
        End If

    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub
Function DoesTABLEExist(DBConnectionString As String) As Boolean

    Try
        Dim conn As MySqlConnection = New MySqlConnection(DBConnectionString)
        ' Dim ADAPTER As New MySqlDataAdapter("Select * From information_schema.tables" &
        '                         " Where table_schema = 'airtech_db' And table_name = 'employees' LIMIT 1;", conn)
        Dim cmd As New MySqlCommand("Select * From information_schema.tables Where table_schema = 'airtech_db' And table_name = 'employees' LIMIT 1;", conn)


        conn.Open()
        Dim bRet As Boolean = False
        Dim reader As MySqlDataReader = cmd.ExecuteReader
        bRet = reader.HasRows
        If (bRet = True) Then
            'MsgBox("Table Exists")
        Else
            ' MsgBox("No more records")
        End If
        conn.Close()
        Return bRet

    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Function

---

这个网站提供了一个问题和答案的预览。如果您在问题看起来像狗的早餐时单击“提交”按钮，您只是不想帮助我们帮助您。错误发生在哪一行？您将需要使用MySqlCommand和ExecuteNonQuery来执行表创建代码。对于某些SQL操作，使用DataAdapter是个坏主意；）请将

“server=localhost；username=root；password=****；”

放入某种可全局访问的字符串中，这样，如果它发生更改，您只需在一个地方更改它，而不需要在很多地方更改。本网站提供了问题和答案的预览，这是有原因的。如果您在问题看起来像狗的早餐时单击“提交”按钮，您只是不想帮助我们帮助您。错误发生在哪一行？您将需要使用MySqlCommand和ExecuteNonQuery来执行表创建代码。对于某些SQL操作，使用DataAdapter是个坏主意；）请将

“server=localhost；username=root；password=****；”

放入某种全局可访问的字符串中，这样，如果它发生更改，您只需要在一个位置更改它，而不需要在很多位置更改它。