如何在新表中将多行数据合并到单列中？

Question

如何将一个表中多行的数据合并到新表中的单个列中？

create table new_paragraphs 
(
    id NUMBER 
    paragraph CLOB 
); 

create table old_paragraphs 
(
    id 
    paragraph CLOB 
); 

merge into new_paragraphs a 
using (select * from old_paragraphs) b 
on (id = id) 
when matched then 
update set a.paragraph = a.paragraph || b.paragraph; 
-- Results in error: unable to get a stable set of rows in the source tables 

上面抛出异常。

Answer 1

如果id均至少* old_paragraphs *（或者，如果它是每个ID唯一在发现了一个主键，它的工作* new_paragraph *）

除此之外，要在on (id = id)使用别名，以便它读取on (a.id = b.id)：

merge into new_paragraphs a 
using (select * from old_paragraphs) b 
on (a.id = b.id) 
when matched then 
update set a.paragraph = a.paragraph || b.paragraph; 

Answer 2

你为什么在这里做MERGE？为什么不是一个简单的UPDATE（假设ID是两个表的主键）

UPDATE new_paragraphs a 
    SET paragraph = (select a.paragraph || b.paragraph 
         from old_paragraphs b 
        where a.id = b.id) 
WHERE EXISTS (SELECT 1 
       FROM old_paragraphs b 
       WHERE a.id = b.id)