Q:

How to document sql query

For a Client of mine I'm documenting an existing database with a few tables and some queries.
For tables I'm using E-R Diagram to show tables and relationships. I'm doing that with DIA Diagram Editor.  
How do I describe and visualize queries? There exist some sort of UML Object to do that?  
So far, I've created a table with query name and a description of what it does and an example screenshot of data retrieved by the query itself. I'm doing that in Word.
I don't like the result of this work, there exist something more professional to do that?  
I wouldn't install new software just know how database designers have to accomplish that task.
EDIT 1
As @Serg suggested I may use view and diagramm the view as an entity. 
If I've understood something like: 

What the client needs is to understand for each query where data come from. 
EDIT 2
I'm doing something like the following:  

Where
driver_tabella_utenti is a TABLE
driver_imp_causali_preparazione is a QUERY
driver_query_riepilogo_prsp is a QUERY  
I think that isn't bast practice! How can I visual design sql queries as I do with entities and relationships?

A:

Short summary
I see 2 options based on specification. This is only based on specification taken literally, not any additional research on the web.

Model class providing an operation representing what the SQL query does. Present a behavior describing this operation as a class stereotyped with <> and with linked object of a type OpaqueBehavior with provided values for attributes body (an SQL query) and language ('SQL').
Model class providing an operation representing what the SQL query does. Provide a note linked to the class containing description of respective OpaqueBehavior (body and language)

I've found another solution in the Specification

Model SQL query as action. The action can be depicted as usually in activity diagram (rectangle with rounded corners) and put SQL directly inside of the rectangle. The action needs to be a part of activity diagram (that is a description of a behaviour that utilizes this SQL).

Explanation
You can use a BehavioralFeature (e.g. Operation) to define that there is some SQL available (it sould be some class that exposes this operation) and then you can define a method with describing OpaqueBehavior (method) that contains body (SQL statement) and language ('SQL').
As specification does not provide any information about notation you can specify it either representing a method as an object (this is a specific instance of OpaqueBehavior) or using a note. In both cases it should be linked to a respective object describing the Behavior provided by the SQL statement as such (e.g. activity).
See 13.2.3.3 of UML Sepcification. Below is just the diagram describing this area.

Edit as a result of further research:
UML Specification describes literally your case in section 16.2 (as OpaqueAction). An example figure 16.8 in section 16.2.5.1 is exactly the case I've described as a 3rd possible answer.

Note however (as already mentioned in comments) that UML is not always the best suitable solution. While I strongly recommend modelling the system using UML, the SQL code itself should be a part of textual documentation that should be created together with the UML diagrams. It will benefit from more clarity, possibility to search, possibility to copy-paste the code etc. Also if your query is more than 2-3 short lines it might even hard to notice that it is still a part of an UML diagram.

