SQLMoreResults allows the application to retrieve multiple sets of result rows. A Transact-SQL SELECT statement containing a COMPUTE clause, or a submitted batch of ODBC or Transact-SQL statements, causes the Microsoft® SQL Server™ ODBC driver to generate multiple result sets. SQL Server does not allow creation of a server cursor to process the results in either case. Therefore, the developer must ensure that the ODBC statement is blocking. The developer must exhaust the returned data or cancel the ODBC statement before he or she can process data from other active statements on the connection.
The developer can determine properties of the result sets columns and rows that are generated by the COMPUTE clause of a SQL Server SELECT statement. For more detail, see SQLColAttribute.
When SQLMoreResults is called with unfetched data rows in the result set, those rows are lost and row data from the next result row set is made available.
void GetComputedRows
(
SQLHSTMT hStmt
)
{
SQLUSMALLINT nCols;
SQLUSMALLINT nCol;
PODBCSETINFO pODBCSetInfo = NULL;
SQLRETURN sRet;
UINT nRow;
SQLINTEGER nComputes = 0;
SQLINTEGER nSet;
BYTE* pValue;
// If SQLNumResultCols failed, then some error occurred in
// statement execution. Exit.
if (!SQL_SUCCEEDED(SQLNumResultCols(hStmt, (SQLSMALLINT*) &nCols)))
{
goto EXIT;
}
// Determine the presence of COMPUTE clause result sets. The SQL
// Server ODBC driver uses column attributes to report multiple
// sets. The column number must be less than or equal to the
// number of columns returned. You are guaranteed to have at least
// one, so use '1' for the SQLColAttribute ColumnNumber
// parameter.
SQLColAttribute(hStmt, 1, SQL_CA_SS_NUM_COMPUTES,
NULL, 0, NULL, (SQLPOINTER) &nComputes);
// Create a result info structure pointer array, one element for
// the normal result rows and one for each compute result set.
// Initialize the array to NULL pointers.
pODBCSetInfo = new ODBCSETINFO[1 + nComputes];
// Process the result sets...
nSet = 0;
while (TRUE)
{
// If required, get the column information for the result set.
if (pODBCSetInfo[nSet].pODBCColInfo == NULL)
{
if (pODBCSetInfo[nSet].nCols == 0)
{
SQLNumResultCols(hStmt, (SQLSMALLINT*) &nCols);
pODBCSetInfo[nSet].nCols = nCols;
}
if (GetColumnsInfo(hStmt, pODBCSetInfo[nSet].nCols,
&(pODBCSetInfo[nSet].pODBCColInfo)) == SQL_ERROR)
{
goto EXIT;
}
}
// Get memory for bound return values if required.
if (pODBCSetInfo[nSet].pRowValues == NULL)
{
CreateBindBuffer(&(pODBCSetInfo[nSet]));
}
// Rebind columns each time the result set changes.
myBindCols(hStmt, pODBCSetInfo[nSet].nCols,
pODBCSetInfo[nSet].pODBCColInfo,
pODBCSetInfo[nSet].pRowValues);
// Set for ODBC row array retrieval. Fast retrieve for all
// sets. COMPUTE row sets have only a single row, but
// normal rows can be retrieved in blocks for speed.
SQLSetStmtAttr(hStmt, SQL_ATTR_ROW_BIND_TYPE,
(void*) pODBCSetInfo[nSet].nResultWidth, SQL_IS_UINTEGER);
SQLSetStmtAttr(hStmt, SQL_ATTR_ROW_ARRAY_SIZE,
(void*) pODBCSetInfo[nSet].nRows, SQL_IS_UINTEGER);
SQLSetStmtAttr(hStmt, SQL_ATTR_ROWS_FETCHED_PTR,
(void*) &nRowsFetched, sizeof(SQLINTEGER));
while (TRUE)
{
// In ODBC 3.x, SQLFetch supports arrays of bound rows or
// columns. SQLFetchScroll (or ODBC 2.x SQLExtendedFetch)
// is not necessary to support fastest retrieval of
// data rows.
if (!SQL_SUCCEEDED(sRet = SQLFetch(hStmt)))
{
break;
}
for (nRow = 0; nRow < (UINT) nRowsFetched; nRow++)
{
for (nCol = 0; nCol < pODBCSetInfo[nSet].nCols;
nCol++)
{
// Processing row and column values...
}
}
}
// sRet is not SQL_SUCCESS and is not SQL_SUCCESS_WITH_INFO.
// If it's SQL_NO_DATA, then continue. If it's an
// error state, stop.
if (sRet != SQL_NO_DATA)
{
break;
}
// If there's another set waiting, determine the result set
// indicator. The indicator is 0 for regular row sets or an
// ordinal indicating the COMPUTE clause responsible for the
// set.
if (SQLMoreResults(hStmt) == SQL_SUCCESS)
{
sRet = SQLColAttribute(hStmt, 1, SQL_CA_SS_COMPUTE_ID,
NULL, 0, NULL, (SQLPOINTER) &nSet);
}
else
{
break;
}
}
EXIT:
// Clean-up anything dynamically allocated and return.
return;
}
| SQLColAttribute | SELECT |