OCP-1Z0-051-V9.02-117题

117. Which statements are true regarding the WHERE and HAVING clauses in a SELECT statement?

(Choose all that apply.)

A. The HAVING clause can be used with aggregate functions in subqueries. 

B. The WHERE clause can be used to exclude rows after dividing them into groups.

C. The WHERE clause can be used to exclude rows before dividing them into groups. 

D. The aggregate functions and columns used in the HAVING clause must be specified in the SELECT list

of the query. 

E. The WHERE and HAVING clauses can be used in the same statement only if they are applied to

different columns in the table. 

Answer: AC

答案解析：

参考：http://blog.csdn.net/rlhua/article/details/12871951

A,having可以用在聚合函数的子句里。正确

B,分组之后不能使用where来限制，因为where只能限制行，不能限制组，错误

C,分组之前可以使用where来限制所要输出的行，正确

D,在having子句的聚合函数或者字段不一定要在select列表中，错误。

E,在同一句子中，where和having可以都使用，可以应用在不同的字段，也可以相同的字段。