Re:문제23.( 의사결정트리2) 분할후 엔트로피를 만들수 있는 SQL 을 작성하시오 !

[6기_이택혁]

select review_yn, count(*) cnt1 , sum(decode(buy_yn,'Y',1,0)) as buy_cnt,

sum(decode(buy_yn,'N',1,0)) as no_buy_cnt

from entropy_test2

group by review_yn;