group: grades dataset
description[[ Dataset for some questions in Ex2

* the relation _Studied_ contains grades of sid per course
* the relation _Course_ contains tid and room per course
* the relation _Teacher_ contains name and department per teacher
]]

Studied = { sid   course   grade
    1, db,   10
    1, web,  7
    1, se,   6.5
    2, db,   4
    2, web,   10
    2, se,   9
    2, ds,   9
    2, prog,8.5
    3, db,   8
    3, web,   10
    3, se,   9
    3, ds,   9
    3, prog,8.5
    4, ds,   6.5
    4, prog, 4
}

Course = {
    course, tid, room
    db,   1,   3
    web,   2,   3
    se,   2,   3
    ds,   3,   2
    prog,   3,   1
}

Teacher = {
    tid, name, dep
    1,  Albert,   math
    2,  Girard,   cs
    3,  Max,   cs
}