Is it possible that SqlException is thrown and property Number == 0?

Question

Is it possible that SqlException will be thrown when trying to execute sql procedure and property Number will be 0?

Specific situation: domain controller is not available/not responding and no real communication with sql server occurred.

Answer 1

No, it should not be possible that SqlException.Number is 0, except for the following cases:

• Read-only routing failure
• Server had severe error processing query
• Processed cancellation while parsing results
• Failed to create user instance

Assuming you're not using read-only routing of SQL Server 2016, then none of these cases could apply to the scenario you described.

Remaining cases are either a non-zero number from sysmessages, or a Win32 error code (which, since 0 == ERROR_SUCCESS, would also never be zero).

In practice you will see something along the lines of "Cannot create SSPI context", or "A transport-level error has occurred when sending the request to the server", or a "An existing connection was forcibly closed by the remote host", and those have nonzero Win32 error codes too.

Reference: https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlerror.number(v=vs.110).aspx

It may be worth noting that SqlException.Number is synonym for the Number property of the first entry in its Errors array, and that array might contain more than one item.

Answer 2

Answering my own question. Yes, it is possible. We added aditional code to catch:

catch (SqlException ex)
{
    for (int i = 0; i < ex.Errors.Count; i++)
    {
        this.logger.Error("Index #" + i + "\n" +
        "Message: " + ex.Errors[i].Message + "\n" +
        "Error Number: " + ex.Errors[i].Number + "\n" +
        "LineNumber: " + ex.Errors[i].LineNumber + "\n" +
        "Source: " + ex.Errors[i].Source + "\n" +
        "Procedure: " + ex.Errors[i].Procedure + "\n");
    }                       

    if (ex.Number == 0)
    {
        this.logger.Warn("Exception was caught but ex.Number == 0! Changing to -69.");
        oResults.Add("_ExitCode", "-69");
    }
}   

and this was logged today.

2017-01-17 08:05:08,282 [r074008903] ERROR ProcessLogger Index #0
Message: A severe error occurred on the current command.  The results, if any, should be discarded.
Error Number: 0
LineNumber: 0
Source: .Net SqlClient Data Provider
Procedure: 

2017-01-17 08:05:08,282 [r074008903] ERROR ProcessLogger Index #1
Message: A severe error occurred on the current command.  The results, if any, should be discarded.
Error Number: 0
LineNumber: 0
Source: .Net SqlClient Data Provider
Procedure: 

2017-01-17 08:05:08,283 [r074008903] WARN  ProcessLogger Exception was caught but ex.Number == 0! Changing to -69.

Because in other place _ExitCode was used to determine is something was wrong in this specific situation we had false information.

Answer 3

It is possible.

I receive 0 when trying to connect SQL which is starting inside ubuntu container. According to this: https://learn.microsoft.com/en-us/sql/relational-databases/errors-events/database-engine-events-and-errors?view=sql-server-ver15 that is undocumented and, probably, is a bug.

Here is my situation, for example: