DBI202Xuất hiện trong 1 đề thi
Given a relation R(A,B,C,D) with the key is A, the foreign key is D. And the query: “select A, count(D) from R group by D” What is the output of the query?
Các lựa chọn
AIt will return all rows from the R table
BIt returns only the A column where the value in D column is grouped
CThis query will cause an error in standard SQL
DThere is no GROUP BY with a HAVING clause.