有三张表关联表：

用户的说说表（ixt_customer_note）

说说的评论表（ixt_customer_note_comment）

评论的回复表（ixt_customer_note_reply）

说说表保存的是用户发表的说说信息，评论表保存的是用户对说说发表的评论信息，回复表保存的是用户对评论及回复的回复

要求查询三张表返回结果为树形结构，如下：

发表说说:1003

发表说说:1002

发表评论:comment1002_1

发表评论:comment1002_2

发表回复:reply_1002_1

发表回复:reply_1002_2

发表评论:comment1002_3

发表说说:1001

发表评论:comment1001_1

发表评论:comment1001_2

发表说说:1000

发表评论:comment1000_1

发表回复:reply_1000_1

发表回复:reply_1000_2

1、设计三张表及插入相关数据

2、分别查出三张表的数据：

2.1、查询用户说说表倒序显示

select createDate, id as dataId, customerId, concat('发表说说:',content) as content from ixt_customer_note order by createDate desc;

2.2、查询说说的评论正序显示

select nc.createDate, nc.dataId, nc.customerId, concat('发表评论:',nc.content) as content from ixt_customer_note_comment nc left join ixt_customer_note n on nc.dataId=n.id order by n.createDate desc, nc.createDate asc;

2.3、查询说说的评论的回复正序显示

select nr.createDate, nc.dataId, nr.customerId, concat('发表回复:',nr.content) as content from ixt_customer_note_reply nr left join ixt_customer_note_comment nc on nr.commentDataId=nc.id left join ixt_customer_note n on nc.dataId=n.id order by n.createDate desc, nc.createDate asc, nr.createDate asc;

3、有了这三张表数据后，如何将他们显示为一张表，最终得到树形结构？

如果想要得到树形展示，可以考虑能否将三张表返回的结果合并为一张表，因为他们的结果合并在一起后正是我们需要的所有数据，只不过最终展示的效果要调整一下。

好的，先考虑合并用户说说及说说的评论，并按树形结构展示，这时我们应该使用 union关键字，求并集。观察一下，合并之后的结果集，应该先根据说说的发表时间倒序，再根据说说的评论的发表时间正序，所以写sql执行一下：

大致的语句为：select * from(说说的结果集 union 评论的结果集) as T order by 说说.createDate desc, 评论.createDate asc;

select * from((select createDate as createDate1, "" as createDate2, id as dataId, customerId, concat('发表说说:',content) as content from ixt_customer_note order by createDate desc) union (select n.createDate as createDate1, nc.createDate as createDate2, nc.dataId, nc.customerId, concat('    发表评论:',nc.content) as content from ixt_customer_note_comment nc left join ixt_customer_note n on nc.dataId=n.id  order by n.createDate desc, nc.createDate asc)) as T order by createDate1 desc, createDate2 asc;

4、上面合并结果集是我们想要的结果，好的，再来合并回复结果集。合并之后的结果集应该按说说的发表时间倒序，再按评论的发表时间正序，再按回复的发表时间正序。为了区分出每条记录是哪张表的，我们在结果集中添加一个字段type，表示记录的类型：t1是说说，t2是评论，t3是回复。

sql语句：select * from(说说的结果集 union 评论的结果集 union 回复的结果集) as T order by 说说.createDate desc, 评论.createDate asc, 回复.createDate asc;

select * from((select createDate as createDate1, "" as createDate2, "" as createDate3, "t1" as type, id as dataId, customerId, concat('发表说说:',content) as content from ixt_customer_note order by createDate desc) union (select n.createDate as createDate1, nc.createDate as createDate2, "" as createDate3, "t2" as type, nc.dataId, nc.customerId, concat('    发表评论:',nc.content) as content from ixt_customer_note_comment nc left join ixt_customer_note n on nc.dataId=n.id  order by n.createDate desc, nc.createDate asc) union (select n.createDate as createDate1, nc.createDate as createDate2, nr.createDate as createDate3, "t3" as type, nc.dataId, nr.customerId, concat('        发表回复:',nr.content) as content from ixt_customer_note_reply nr left join ixt_customer_note_comment nc on nr.commentDataId=nc.id left join ixt_customer_note n on nc.dataId=n.id order by n.createDate desc, nc.createDate asc, nr.createDate asc)) as T order by createDate1 desc, createDate2 asc, createDate3 asc;

5、上面结果集是我们想要的，不过createDate最终应该只有一个，可以继续改进，将createDate合并为一列，说说显示createDate1，评论显示createDate2，回复显示createDate3。

改进后的语句如下：

select if(T.type='t1',T.createDate1,(if(T.type='t2',T.createDate2,T.createDate3))) as createDate, T.type, T.dataId, T.customerId, T.content from((select createDate as createDate1, "" as createDate2, "" as createDate3, "t1" as type,customerId, id as dataId, concat('发表说说:',content) as content from ixt_customer_note order by createDate desc) union (select n.createDate as createDate1, nc.createDate as createDate2, "" as createDate3, "t2" as type, nc.customerId, nc.dataId, concat('    发表评论:',nc.content) as content from ixt_customer_note_comment nc left join ixt_customer_note n on nc.dataId=n.id  order by n.createDate desc, nc.createDate asc) union (select n.createDate as createDate1, nc.createDate as createDate2, nr.createDate as createDate3, "t3" as type, nr.customerId, nc.dataId, concat('        发表回复:',nr.content) as content from ixt_customer_note_reply nr left join ixt_customer_note_comment nc on nr.commentDataId=nc.id left join ixt_customer_note n on nc.dataId=n.id order by n.createDate desc, nc.createDate asc, nr.createDate asc)) as T order by createDate1 desc, createDate2 asc, createDate3 asc;

好的，到此content返回的结果为我们最终想要的结果了！

6、补充：如果要根据说说id求出对应的评论及回复列表：

求说说id=1000的评论及回复sql语句如下：

select if(T.type='t2',T.createDate2,T.createDate3) as createDate, T.type, T.dataId, T.customerId, T.content from((select nc.createDate as createDate2, "" as createDate3, "t2" as type, nc.customerId, nc.dataId, concat('发表评论:',nc.content) as content from ixt_customer_note_comment nc where nc.dataId='1000' order by nc.createDate asc) union (select nc.createDate as createDate2, nr.createDate as createDate3, "t3" as type, nr.customerId, nc.dataId, concat('    发表回复:',nr.content) as content from ixt_customer_note_reply nr left join ixt_customer_note_comment nc on nr.commentDataId=nc.id where nc.dataId='1000' order by nc.createDate asc, nr.createDate asc)) as T order by createDate2 asc, createDate3 asc;