手册/文件广泛使用“内袋”和“外袋”的语言(例如:http://pig.apache.org/docs/r0.11.1/basic.html ),但我还没能明确区分这些术语的确切定义。
e、 g.所有内在的相互关联:
如果我给你一个袋子“foo”,你需要知道什么才能把foo标记为“内袋”而不是“外袋”?
不是最外层袋子的“任何袋子”是“内层袋子”吗?
内部和外部的标签总是排他性的吗?
在古拉丁语中,所有的“包”都是“关系”,还是只有“最外层的包”是一种关系(与内袋无关)
创建一个可讨论的示例:
grunt> dump A;
(1,2,3)
(4,2,1)
(8,3,4)
(4,3,3)
grunt> W1 = GROUP A ALL;
grunt> W2 = GROUP W1 ALL;
grunt> W3 = GROUP W2 ALL;
grunt> W4 = GROUP W3 ALL;
grunt> describe W4;
W4: {group: chararray,W3: {(group: chararray,W2: {(group: chararray,W1: {(group: chararray,A: {(f1: int,f2: int,f3: int)})})})}}
grunt> illustrate W4;
(1,2,3)
---------------------------------------------------
| A | f1:int | f2:int | f3:int |
---------------------------------------------------
| | 1 | 2 | 3 |
| | 8 | 3 | 4 |
---------------------------------------------------
------------------------------------------------------------------------------------------------
| W1 | group:chararray | A:bag{:tuple(f1:int,f2:int,f3:int)} |
------------------------------------------------------------------------------------------------
| | all | {(1, 2, 3), (8, 3, 4)} |
------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------------------------------------------
| W2 | group:chararray | W1:bag{:tuple(group:chararray,A:bag{:tuple(f1:int,f2:int,f3:int)})} |
-----------------------------------------------------------------------------------------------------------------------------------------------
| | all | {(all, {(1, 2, 3), (8, 3, 4)})} |
-----------------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| W3 | group:chararray | W2:bag{:tuple(group:chararray,W1:bag{:tuple(group:chararray,A:bag{:tuple(f1:int,f2:int,f3:int)})})} |
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| | all | {(all, {(all, {(1, 2, 3), (8, 3, 4)})})} |
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| W4 | group:chararray | W3:bag{:tuple(group:chararray,W2:bag{:tuple(group:chararray,W1:bag{:tuple(group:chararray,A:bag{:tuple(f1:int,f2:int,f3:int)})})})} |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| | all | {(all, {(all, {(all, {(1, 2, 3), (8, 3, 4)})})})} |
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
grunt> dump W4;
(all,{(all,{(all,{(all,{(1,2,3),(4,2,1),(8,3,4),(4,3,3)})})})})
在这些袋子里——w1,w2,w3,w4——哪个在里面,哪个在外面?
1条答案
按热度按时间klsxnrf11#
外袋其实是关系
A
. 这有点奇怪,但一旦你知道什么是内袋,你就会明白了。让我们看看W1
,以便于阅读,因为嵌套的袋子不会改变答案。的架构和输出
W1
:我们可以看到他们是一个领域
W1
命名A
这是一个袋子。这是一个内部包,因为包是关系中的一个字段。请记住,包只是无序的元组集,我们可以看到这是的输出
W1
. 现在,看看关系的输出A
:pig不保证这些元组的顺序(除非
ORDER
或者别的什么)。所以,如果你仔细想想A
实际上只是一组无序的元组。这是一个外袋。你可以在这里找到一些这样的例子。