Fixed parameter generation and added SQL query helper

Not exactly sure why your parameter generation didn't work for me, but I've added a rather hackinsh solution for now. 

Also added showQuery method that you may want to use. 

Previously all parameters were named p1, because $parameters->containsKey($parameterName) didn't work as intended. 


could you use PSR-2 code convention:

```php
private function getUsedParameterNames()
{
   ...
}
```