I have two tables "main parent" and "children". When I create a "main parent" it maight have 0 to many children. If the "main parent" has children, I have to compute the number of boys with an age than more 12 years old.
How can I do that ?
Sounds like a homework assignment.. LOL..
Check out the manual .. https://ninoxdb.de/en/manual/calculations/reference-of-functions-and-language and search for "age(Birthdate)".
Basically .. you just want to search the children where age(Birthdate) > 12. If you do it as a "composite" table, Ninox will take care of the foriegn key relaionship... If not a composite table.. then make sure to also use the "main parent" primary key = "children" foriegn key. There is a little hidden gem that if using the Ids.. you can use number("main parent".Id) = number(children.Parent.Id)..
Finally, Julian Kirkness has posted a few blogs that you may find useful. (THANKS JULIAN!!!!)
Relating to Relational Databases parts 1 and 2