[stanford]Introduction to databases （week2）

DreamBoy 发表于 2014-1-13 23:08
Find the names of all females who eat at least one pizza served by Straw Hat. (Note: The pizza need  ...

i have the same problem here. my error message said that :

Error from SQLite: Error validating subquery:

\select_{gender = 'female' and pizzeria= 'Straw Hat'} <- ERROR!

Person <- output schema: RA_TMP_VIEW_1(name text, age integer, gender text)

Error message: no such column: pizzeria

Error code: 0

SQL state: null

i don't understand why.

my answer is:
\project_{name} ( \select_{gender = 'female' and pizzeria= 'Straw Hat'} Person \join Frequents)

gougou9901 发表于 2014-1-18 23:53
谢谢你啊！我刚才终于知道怎么做了！先把符合条件的pizza以及对应的供应商弄出来，得到relationA(pizzeri ...

亲，能不能麻烦你再解释下。到这一步：
“这个relation中每个pizzeria对应两种pizza，再用relationB \diff relationA 得到的就是只serve一种pizza的pizzeria”

我得到的是一个空集。
因为relationB(pizzeria,pizza) 里得到的供应商是全部供应商。 R(a)里也是。

想问下relationB \diff relationA  到底是什么变量diff什么变量呢？？谢谢~