7장 집합

1)

   /**
     * JPQL
     * select
     *      COUNT(m), // 회원수
     *      SUM(m.age), // 나이 합
     *      AVG(m.age), // 평균 나이
     *      MAX(m.age), // 최대 나이
     *      MIN(m.age), // 최소 나이
     * from Member m
     */
    @Test
    public void aggregation() throws Exception{

        List<Tuple> result = queryFactory
                .select(
                        member.count(),
                        member.age.sum(),
                        member.age.avg(),
                        member.age.max(),
                        member.age.min()
                        )
                .from(member)
                .fetch();

        Tuple tuple = result.get(0);
        assertThat(tuple.get(member.count())).isEqualTo(4);
        assertThat(tuple.get(member.age.sum())).isEqualTo(100);
        assertThat(tuple.get(member.age.avg())).isEqualTo(25);
        assertThat(tuple.get(member.age.max())).isEqualTo(40);
        assertThat(tuple.get(member.age.min())).isEqualTo(10);
    }

    /**
     * 팀의 이름과 각 팀의 평균 연령을 구하라
     */
    @Test
    public void group() throws Exception{
        List<Tuple> result = queryFactory
                .select(team.name, member.age.avg())
                .from(member)
                .join(member.team, team)
                .groupBy(team.name)
                .fetch();

        Tuple teamA = result.get(0);
        Tuple teamB = result.get(1);

        assertThat(teamA.get(team.name)).isEqualTo("teamA");
        assertThat(teamA.get(member.age.avg())).isEqualTo(15);

        assertThat(teamB.get(team.name)).isEqualTo("teamB");
        assertThat(teamB.get(member.age.avg())).isEqualTo(35);
    }

2)

groupBy , 그룹화된 결과를 제한하려면 having

.groupBy(item.price)
.having(item.price.gt(1000))