如何在try catch塊中捕獲MySQL錯誤？

Question

我想在MySQL數據庫上執行查詢。我已經把try命令放在一個try catch塊中，但是當查詢失敗時它仍然會拋出一個異常。我該如何防止並簡單地捕捉錯誤？

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() 

如果列已經存在，它拋出一個錯誤，但如果沒有，那麼一切都很好，和查詢被執行，程序繼續下去。

Answer 1

如果您要捕捉異常，您應該捕捉查詢的整個代碼，因爲連接也可能失敗。

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 

編輯：

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 

編輯

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