Add Lives

$GLOBALS['TYPO3_DB']->store_lastBuiltQuery = 1;

// process query
$res = $GLOBALS['TYPO3_DB']->exec_SELECTquery($select_fields,$from_table,$where_clause,$groupBy,$orderBy,$limit);

// the complete SQL-Statement
echo $GLOBALS['TYPO3_DB']->debug_lastBuiltQuery;