mysql - 如何在 try catch block 中捕获 MySQL 错误？

Question

我正在尝试对 MySQL 数据库执行查询。我已经将执行命令放在 try catch block 中，但是当查询失败时它仍然会抛出异常。我该如何防止这种情况并简单地捕获错误？

Dim db_connection As String = my_connection_string
Dim MyConn As OdbcConnection  
MyConn = New OdbcConnection(db_connection)
Dim MyCommand As New OdbcCommand()
Dim myReader As OdbcDataReader = Nothing
MyCommand.Connection = MyConn
MyConn.Open()

query = "Alter table Table1 ADD COLUMN `col_2` VARCHAR(50) AFTER `col_1`"
MyCommand.CommandText = query
try
     myReader = MyCommand.ExecuteReader()
catch ex as Exception
     output(ex.tostring)
end try
myReader.Close()

如果该列已经存在，它会抛出一个错误，但如果它不存在，那么一切都很好，查询得到执行，程序继续。

Answer 1

如果您要捕获异常，您应该捕获查询的整个代码，因为连接也可能失败。

Dim db_connection As String = my_connection_string
Dim MyConn As OdbcConnection  
Dim MyCommand As New OdbcCommand()

try
     MyConn = New OdbcConnection(db_connection)
     MyCommand.Connection = MyConn
     MyConn.Open()
     query = "Alter table Table1 ADD COLUMN `col_2` VARCHAR(50) AFTER `col_1`"
     MyCommand.CommandText = query
     MyCommand.ExecuteNonQuery()
catch ex as Exception
     output(ex.tostring)
end try

编辑:

Try
    Using connection As New OdbcConnection(my_connection_string)
        query = "Alter table Table1 ADD COLUMN `col_2` VARCHAR(50) AFTER `col_1`"
        Using command As New OdbcCommand(query, connection)
            connection.Open()
            command.ExecuteNonQuery()
        End Using   
    End Using
Catch ex As Exception
    Console.WriteLine(ex.Message)
End Try

编辑

Try
    'code here
Catch exception As OdbcException
    Console.WriteLine(exception.Message)
Catch ex As Exception
    Console.WriteLine(ex.Message)
End Try