when i tray use group by it git me a lot of errors and i do not way that, and how can i group data without getting me an error
After doing a Group, you no longer have the Entities that existed before.
Only the ones in Output (the left column). In this example, no more Order.*, only id_Order.
That is part of the training.
Hello Ahmed,
You need to change the values in the expression as well. You can see the error is "Can't identify Order element". It is because you will get output of only grouped columns and you have to use those columns in your expression as well