ITPub博客

首页 > Linux操作系统 > Linux操作系统 > 047-134

047-134

原创 Linux操作系统 作者:jbymy2000 时间:2012-03-19 10:04:56 0 删除 编辑
134. Which two statements are true regarding subqueries? (Choose two.)
A. Only two subqueries can be placed at one level.
B. A subquery can be used to access data from one or more tables or views.
C. If the subquery returns 0 rows, then the value returned by the subquery
expression is NULL.
D. The columns in a subquery must always be qualified with the name or alias
of the table used.
E. A subquery in the WHERE clause of a SELECT statement can be nested up to
three levels only.
Answer: BC
Qualify:限制
SQL> select decode((select revenue from test where dest='dd'),null,11) dest
from test;
DEST
----------
11
说明如果子查询返回0行,则整个返回值为空

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/11312660/viewspace-718953/,如需转载,请注明出处,否则将追究法律责任。

上一篇: 047-133
下一篇: 047-135
请登录后发表评论 登录
全部评论

注册时间:2012-01-10

  • 博文量
    416
  • 访问量
    203062