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drop table if exists articles;

CREATE table articles (ID int auto_increment primary key,title varchar), Postuser varchar, postdate datetime,parent ID int references articles (ID));

INSERT INTO articles values

(NULL, ' first ' , ' Zhang San ', ' 1998-10-10 12:32:32 ', null),

(NULL, ' second ' , ' Zhang San ', ' 1998-10-10 12:34:32 ', null),

(NULL, ' first reply 1 ', ' John Doe ', ' 1998-10-10 12:35:32 ', 1),

(NULL, ' second reply 1 ', ' John Doe ', ' 1998-10-10 12:36:32 ', 2),

(NULL, ' first reply 2 ', ' Harry ', ' 1998-10-10 12:37:32 ', 1),

(NULL, ' first reply 3 ', ' John Doe ', ' 1998-10-10 12:38:32 ', 1),

(NULL, ' second reply 2 ', ' John Doe ', ' 1998-10-10 12:39:32 ', 2),

(NULL, ' first reply 4 ', ' Harry ', ' 1998-10-10 12:39:40 ', 1);

Here are two ways to get results in MySQL:

1.

Select A.title,a.postuser,
(select Max (postdate) from articles where parentid=a.id) reply
From articles a where a.parentid is null;

2.select E.title,e.postuser,ep.postdate from Articles E,

(select Max (postdate) postdate,

ParentID

From articles

where

ParentID is not NULL

Group by ParentID) EP

where ep.parentid=e.id

In Netezza, such as: The first way will be an error to rewrite, so in Netezza we want to use the second way to query

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