I'm using Odoo version 7. Pgadmin 4 to read the database. 

yes, The quantity on hand from product. this is the available quantity in the warehouse found in the menu wharehouse --> products and the tab inventory.

the inscription in  developer mode is :

Field : qty_available

object : product.product

type : float

Modifiers :{"readonly":true}

 in the table product_product, the field qty_available doesn't exist.

to Pat answer :

thank you pat, if i can get it through a sql query what should i write? "SELECT qty_available FROM product_product" can't work.

Sorry i can't write an other answer, so i edit , this one...

Thank you for your help , but i'm a beginner and i don't know where i can find the files python and how to modify it.

By the way, i found a solution using the table stock_move,  and subtract the entries with the issues , it result the quantity in hand.

Thank you for your help.

Dear Paulo, 

I used 2 queries, made the query easier :

query 1 (entry):

SELECT product_id, Sum(product_qty)

FROM stock_move W

WHERE (location_dest_id=12)

GROUP BY product_id;

query 2 (issue): 

SELECT product_id, Sum(product_qty)

FROM stock_move

WHERE view_src_location Like '12'

GROUP BY product_id;

And via excel subtract the entry with issues.

It's working but there are some movement on the DB who are not in Odoo interface who create some qty mistake.

I know it's not the best way to do, but as a beginner it's all i found according my knowledge.

I'll appreciate if you can add +1 to my answer to raise my karma to 8 to be able to comment in the right place in the forum.