Question

I have the following SQL statement:

USE "ws_results_db_2011_09_11_09_06_24";SELECT table_name FROM INFORMATION_SCHEMA.Tables WHERE table_name like 'NET_%_STAT' order by table_name

I am using the following C++ code to execute it:

IDBCreateCommandPtr spDBCreateCommand = GetTheDBCreateCommandPointer();
ICommandTextPtr spCommandText;
spDBCreateCommand->CreateCommand(NULL, IID_ICommandText, reinterpret_cast<IUnknown **>(&spCommandText));
spCommandText->SetCommandText(DBGUID_SQL, GetTheQueryText());
IRowsetPtr spRowset;
spCommandText->Execute(NULL, IID_IRowset, NULL, NULL, reinterpret_cast<IUnknown **>(&spRowset));
RowHandles hRows(spRowset, 0);
ULONG   rowCount;
ULONG maxRowCount = 1;
spRowset->GetNextRows(DB_NULL_HCHAPTER, 0, maxRowCount, &rowCount, hRows.get_addr());

Two notes:

1. Error handling is omitted for brevity
2. RowHandles implements the RAII concept for HROW *

Anyway, I fail to execute the two SQL statements. What happens is that spCommandText->Execute returns S_OK, but sets spRowset to NULL.

If I execute the same spCommandText->Execute the second time (by moving back the instruction pointer during the debugging session), then a valid IRowset pointer is returned – I successfully obtain the correct column information using it. But spRowset->GetNextRows sets rowCount to 0 and returns DB_S_ENDOFROWSET – no luck.

The code is working fine when I execute a single SQL statement.

What am I doing wrong?

Thanks.

Answer 1

It is up to the client to split the sql commands – isql does this on the ; ie you are asking for two commands the use and the select.
So the fix is to do the two commands by separate sets of CreateCommands and execute.

Also note in this case you can do the commands as one SQL statement

SELECT table_name FROM ws_results_db_2011_09_11_09_06_24.INFORMATION_SCHEMA.Tables 
  WHERE table_name like 'NET_%_STAT' 
  order by table_name