xcode sqlite delete row in one table where EXISTS in another table - objective-c

Question

When I run the following code to delete a row from the MAIN.NOTES table, if tasks.todoDone does not have a match nothing is deleted in MAIN.NOTES. But if one tasks.todoDone is greater than '' then all the rows in MAIN.NOTES are deleted even if task.todoNod is not less than nod.
The second part of the code, deleting from MAIN.TASKS works correctly and only deletes rows that match both tests.
What do I have wrong in my EXISTS (select * line?
if (sqlite3_open(dbpath, &tasksDB) == SQLITE_OK) {
NSString *querySQLNotes = [NSString stringWithFormat:#"DELETE FROM MAIN.NOTES WHERE EXISTS (select * from MAIN.TASKS where tasks.todoNod <'%i' and tasks.todoDone > '')",nod];
char *errMsg;
const char *query_stmtN = [querySQLNotes UTF8String];// this should delete the notes for task that will be deleted next
if (sqlite3_exec(tasksDB, query_stmtN, NULL, NULL, &errMsg) == SQLITE_OK) {
int tc = sqlite3_changes(tasksDB);
NSLog(#"total count of deleted notes %i",tc);
}
NSString *querySQL = [NSString stringWithFormat:#"DELETE FROM MAIN.TASKS WHERE todoNod <'%i' and todoDone > ''",nod];
const char *query_stmt = [querySQL UTF8String];
if (sqlite3_prepare_v2(tasksDB, query_stmt, -1, &statement, NULL) == SQLITE_OK) {
if (sqlite3_step(statement) == SQLITE_DONE) {
NSLog(#"Match found and deleted");
} else {
NSLog(#"Match found and not deleted");
}
sqlite3_finalize(statement);
int tc = sqlite3_changes(tasksDB);
NSLog(#"total count of deleted tasks %i",tc);
}
sqlite3_close(tasksDB);
}
Thanks