Is it possible to use aggregate functions and property in Projections, Criteria, Grails?

Question

I am using Grails Criteria (similar to hibernate criteria) to get a list of Student who got highest grade in each division from the given table. And I want ONLY Name, Division and Grade fields.

Name | Division | Grade | Std_id
---------------------------------
AA1  | A        |  2     | 1
AA2  | A        |  4     | 2
BB1  | B        |  2     | 3
BB2  | B        |  5     | 4

The result I want is

Name | Division | Grade |
--------------------------
AA2  | A        |  4     |
BB2  | B        |  5     | 

if I use the following criteria

    def criteria = Student.createCriteria()
    def resultlt = criteria.list {
        projections {
            groupProperty('divison')
            max('grade')             
        }
    }

I got ONLY Division and Grade, other fields are not included. I need Name field as well.

If I changed the criteria (used aggregate functions and property together in projections) to

    def criteria = Student.createCriteria()
    def resultlt = criteria.list {
        projections {
            property('name')
            groupProperty('divison')
            max('grade')

        }
    }

It give the following error..

ERROR: column "this_.name" must appear in the GROUP BY clause or be
 used in an aggregate function
  Position: 63. Stacktrace follows:
org.postgresql.util.PSQLException: ERROR: column "this_.name" must
appear in the GROUP BY clause or be used in an aggregate function
  Position: 63
        at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryEx
ecutorImpl.java:2161)
        at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutor
Impl.java:1890)
        at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.ja
va:255)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Stat
ement.java:559)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(Abstract
Jdbc2Statement.java:417)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc
2Statement.java:302)

Answer 1

I think there is no way to get answer using createCriteria but I tried something else, Please try it:

def studentList = Student.executeQuery("from Student A where A.Grade in (select max(B.Grade) from Student as B group by B.Division)")

Answer 2

This is a common aggregation problem. the selected fields must appear in the GROUP BY clause[*]. As I can see your Division column and Name column combination are incomparable so you need to do it in another way. I think you need subquery for the above condition .