Hi, i wouldlike to use aggregate functions in HQL, and i got such problems
while experimenting with the query...
i have a class Booking like
Booking(id, tutor,week,package,date,fee,term,note,student,order)
i wouldl like to do a query as such : "
"SELECT DISTINCT tutor, week, COUNT(DISTINCT student) AS numOfStudents
FROM Booking WHERE term=:tm GROUP BY
tutor,week"
problem 1 is - the query does not work because i got an error telling me
that group by clause must include all variables of this Booking class, i e ,
i changed my query to
"SELECT DISTINCT tutor, week, COUNT(DISTINCT student) AS numOfStudents
FROM Booking WHERE term=:tm GROUP BY
tutor,week, id, package, date,fee,term,note,student,order"
and it works. however, it seems that the query produces a list of Booking
objects, not only the variables tutor, week, and numOfStudents as specified
in the SELECT clause. as a result i got 2nd problem
problem 2 - i actually defined another class called "Rota(tutor, week,
numOfStudents)"
and i did
Rota t = (Rota) queryResult.get(0);
and i got a ClassCastException. i guess the reason is that the query
produces a list of Booking objects other than the only selected variables as
in the select clause; therefore i changed to
Booking b =(Booking) queryResult.get(0);
unsurprisingly it doesnt work i guess its because in the select clause i
have another variable "numOfStudnets" which is not defined in Booking.
i dont know what to do... i certainly donot want to add a variable of
"numOfStudent" to Booking class.. but i dont know any other solutions to
this problems. seems HQL makes aggregate query much more complicated, or im
doin this in totally wrong way?
all in all, all i want to do is to get the values of "tutor, week, and
numberOfStudents" from the query, nothing else.
any ideas please help! thank you.
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