Set input variable value and let user to choose from select box of possibile values

It could be interesting to let define a variable and possible values.

The possible values have to be shown in a select box.

Example
:messageTypeId can be one of these values:

- 'type1'
- 'type2'
- 'type3'

```
SELECT * FROM mytable
WHERE type_id == :messageTypeId;
```