Thanks Olegk for your answer.
Just for your information, I want to use JQgrid with joomla.
In fact, I should verify that the user id is authorised to consult the data of the groupe with id 105. If not, an error message will be displayed.
I have a datasource.php where the query is coded to access to the database to retrieve the data for my grid.
Is it in this file that I have to code the request that userid and groupeid are compatible just before my query for the data?
To get the user id, I usually use in joomla