4、choose two:
View the Exhibit and examine the data in the PRODUCT_INFORMATION table.
Which two tasks would require subqueries? (Choose two.)

A) displaying all supplier IDs whose average list price is more than 500
B) displaying the total number of products supplied by supplier 102071 and having product status
OBSOLETE
C) displaying all the products whose minimum list prices are more than the average list price
of products having the product status orderable
D) displaying the number of products whose list prices are more than the average list price
E) displaying the minimum list price for each product status

Answer：CD

解析：子查询用在查询未知的值。
C 的答案类似于：
SQL> select sal from emp where sal > (select avg(sal) from emp where job='SALESMAN');

D 的答案类似于：
SQL> select count(*) from emp where sal > (select avg(sal) from emp);