问一个左连接的问题。。。

2011-05-23 09:57:30 205 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

PaddleOCR实战：DBnet++与DBnet模型训练全流程解析本文详细解析了基于PaddleOCR框架的DBnet与DBnet++文字检测模型的完整训练流程。从环境配置、数据集准备、配置文件解读，到模型训练、评估调参及最终推理部署，提供了实战指南。重点对比了DBnet++与DBnet在精度、速度及适用场景上的差异，帮助开发者高效构建定制化的OCR检测模型。阅读详情

A表
id name
1 test1
2 test2
3 test3

--------------------------------------------
B表
id name code
11 test1 '001'
12 test1 '002'
13 test2 '004'

--------------------------------------------
oracle数据库：
select a.id,b.code
from A a left join B b
on a.name = b.name;

查出的数据为：
a.id b.code
1 '001'
1 '002'
2 '004'
3 null

------------------------------------------------

如何用左连接使查询出的数据为：
a.id b.code
1 '001'
2 '004'
3 null

谢谢！！

...全文

2. Netty使用JSerialComm进行串口读取（二）现在开始处理这些问题第一个问题：串口读取超时异常一路传播到最后也没有处理。第二个问题：即使处理了该异常，程序仍然退出，这不能满足一些实际使用要求需求。该问题与设置很长的读取超时时间没关系，无论多长到时间后总会退出。阅读详情

wlalw131415

Oracle 17,133 成员 55,258 内容

+ 关注 + 加入社区

切换为时间正序

Kobayashi 2011-05-23

打赏
举报

select * from (select a.id,a.name,b.Code from A a ,B b where a.name =b.name(+) ) d ,(select distinct a.id,a.name from A a ,B b where a.name= b.name) e where d.id = e.id

BlueskyWide 2011-05-23

打赏
举报

select c.id, c.code, c.updatetime

  from (select a.id, a.name, b.code, b.updatetime

          from a, b

         where a.name = b.name(+)) c

 where not exists (select 1

          from b

         where b.name = c.name

           and b.code < c.code);

tangren 2011-05-23

打赏
举报

--先连接，再去重

SELECT *

  FROM (SELECT a.id, a.name, b.code FROM a LEFT JOIN b ON a.name = b.name) c

 WHERE NOT EXISTS (SELECT 1

          FROM b

         WHERE b.name = c.name

           AND b.code < c.code);

--先去掉重复，再连接           

SELECT a.id, a.name, c.code

  FROM a

  LEFT JOIN (SELECT *

               FROM b

              WHERE NOT EXISTS (SELECT *

                       FROM b b1

                      WHERE b.name = b1.name

                        AND b.code > b1.code)) c

    ON a.name = c.name;

wlalw131415 2011-05-23

打赏
举报

顶一下！

秋雨飘落 2011-05-23

打赏
举报

select a.id,nvl(b.code,'null'),nvl(b.updatetime,'null')
from A a left join B b
on a.name = b.name;

select a.id,nvl(b.code,'null'),nvl(b.updatetime,'null')
from A a , B b
where a.name = b.name(+);

jumpheightway 2011-05-23

打赏
举报

a-b
b-a

304的的哥 2011-05-23

打赏
举报



SQL> with ta as(

  2       select 1 id,'test1' name from dual union all

  3       select 2,'test2' from dual union all

  4       select 3,'test3' from dual)

  5  ,tb as(

  6      select 11 id,'test1' name,'001' code from dual union all

  7      select 12,'test1','002' from dual union all

  8      select 13,'test2','004' from dual)

  9  select id,nvl(code,'null') code

 10  from (

 11       select row_number() over (partition by ta.id order by ta.id) r_id,

 12              ta.id id,tb.code code

 13       from ta,tb

 14       where ta.name=tb.name(+))

 15  where r_id=1

 16  /

 

        ID CODE

---------- ----

         1 001

         2 004

         3 null

问一个左连接的问题。。。

相关推荐