从SQL表中删除行（日期和时间值错误）

Question

I try to write and then delete from an SQL table. My WRITE code is OK, however my DELETE code does not work as I want.

//SQL_ConnectionString defined above
SqlConnection SQL_Connection = new SqlConnection(SQL_ConnectionString)

string   INSERT =  "INSERT INTO " + tbTable_DAQ.Text + " (Date, Time, Comment)";
string   VALUES =  "VALUES " + " (@Date,    @Time,   @Comment)";
string   SQL_WriteString =  INSERT + VALUES;

DateTime DateTimeNow = DateTime.Now;

try
{
   //get time
   DateTimeNow = DateTime.Now;

   //create SQL command object
   SqlCommand SQL_Write = new SqlCommand(SQL_WriteString, SQL_Connection);

   //attach values
   SQL_Write.Parameters.AddWithValue("@Date", DateTimeNow);
   SQL_Write.Parameters.AddWithValue("@Time", DateTimeNow);
   SQL_Write.Parameters.AddWithValue("@Comment", "Table Access Test. ");

   SQL_Write.ExecuteNonQuery();

   //dispose & nullify SQL_Write
   SQL_Write.Dispose();
   SQL_Write = null;
}

catch (Exception eWrite) 
{ 
   MessageBox.Show(eWrite.ToString(), "SQL WRITE ERROR", MessageBoxButtons.OK, 
                                       MessageBoxIcon.Exclamation); 
}

//now delete inserted row from SQL table            
string DELETE = "DELETE FROM " + tbTable_DAQ.Text + " ";
string FROM =  "WHERE " + "Date = " + DateTimeNow  + "AND " + "Time = " + DateTimeNow 
               + "AND " + "Comment='Table Access Test.'"; //not working
string   SQL_DeleteString  = DELETE + FROM;

try 
{ 
   //create SQL command object
   SqlCommand SQL_Delete = new SqlCommand(SQL_DeleteString, SQL_Connection);
   SQL_Delete.ExecuteNonQuery();
   //dispose & nullify SQL_Delete
   SQL_Delete.Dispose();
   SQL_Delete = null;
}

catch (Exception eDelete)     
{ 
     MessageBox.Show(eDelete.ToString(), "SQL DELETE ERROR", MessageBoxButtons.OK, 
                       MessageBoxIcon.Exclamation); 
}

It give me an error. I believe the error is due to the values of the Date and Time column. On the WRITE code, I think the SQL table converts DateTimeNow to on receiving it on the Date (date type) and Time (time7 type). However, to delete that specific row the values must match (no conversion is done) and I do not know how to get the values right.

Answer 1

You are checking against datetime values that are very specific. Unless you have tables records that are EXACTLY the same date and time, this will never work.

Also, you are checking both what I assume is a date field and a time field against a datetime. Why aren't you just comparing one datetime field?

Answer 2

Your insert works becuase you're using SQL parameters to pass values to SQL which is great. Your DELETE probably fails on a Syntax error (it would be nice if you included the text of the error) because you're building a string and trying to execute it.

You can probably fix the delete-string by putting single-quotes around your dates but I don't even want to show you the right syntax. I'd rather you use SQL parameters again for two BIG reasons:

1. SQL will do the right conversion for you - no worries about getting the text right.
2. You're protecting yourself from SQL injection - a MAJOR security problem caused by building SQL strings and executing them.

Answer 3

Please try sending the DateTime.Now formatted to Sql proc as string

eg like this

string formatted = dateNow.ToString("yyyyMMdd");

Answer 4

If your autocommit isnt on you should type connection.transaction.commit. I think it would be better if you catch a status and finally test like this:

finally
{
  if (status)
  {
    connection.transaction.commit;
  }
  else
  {
    connection.transaction.rollback;
  }
}

Maybe your code try to delete a row which isnt inserted because of no commit. But normaly it should be the datetime problem ;-)

Answer 5

Alright, So base on n8wrl's suggestion, I do not use the strings for my SQL DELETE code. I changed it to:

        //now delete inserted row from SQL table            
        string DELETE = "DELETE FROM " + tbTable_DAQ.Text + " ";
        string FROM = "WHERE " + "Date = @Date" + " AND " + "Time = @Time" + " AND " + "Comment = @Comment";
        string SQL_DeleteString = DELETE + FROM;

        try
        {
           //create SQL command object
           SqlCommand SQL_Delete = new SqlCommand(SQL_DeleteString, SQL_Connection);

           //attach values
           SQL_Delete.Parameters.AddWithValue("@Date",               DateTimeNow.Date);
           SQL_Delete.Parameters.AddWithValue("@Time",               DateTimeNow.TimeOfDay);
           SQL_Delete.Parameters.AddWithValue("@Comment",            "Table Access Test.");

           SQL_Delete.ExecuteNonQuery();

           //dispose & nullify SQL_Delete
           SQL_Delete.Dispose();
           SQL_Delete = null;
        }

        catch (Exception eDelete) { MessageBox.Show(eDelete.ToString(), "SQL DELETE ERROR", MessageBoxButtons.OK, MessageBoxIcon.Exclamation); }

and things work fine. Thanks to Hatsoft for your help. I think it is best to avoid the messy string method. I do not want any injection attack. I will be any MAJOR problem if that happens. I mean, REALLY MAJOR.

Answer 6

There are two different DateTimeNow variables that likely contain two slightly different values which would make an "exact match" fail.

Remove the nested one in the try/catch of the UPDATE that shadows the outer variable; I suspect it might "work" then.

However, it generally is an error to look for such an "exact" time. Perhaps you mean to look for "with the same minute" or similar?

Also, where are both the DATE and TIME columns being fed a DateTime? And what DB types do they represent?

And please fix the DELETE to use parameters like the UPDATE does .. there is no point regressing to not using parameters when the .NET framework handles them rather well.