민희의 코딩일지

SQL Data Type *SQL은 대, 소문자 구별하지 않는다! pure relational algebra - removes all duplicates multiple relational algebra, SQL - ratains duplicates relation algebra to SQL select A1, A2, .., An from r1, r2, .., rm where P sql to relation algebra → π A1, A2, .., An ( σ p ( r1 x r2 x .. x rm ) ) // select엔 group by에 쓴 애트리뷰트 + aggregation만 쓸 수 있음 select A1, A2, sum(A3) from r1, r2, .., rm where p group by ..