Question

我在Oracle数据库中有以下两个表（只读访问权限，所以我只能使用select）。

Question表：

N   Question ID
1   1
2   2
3   3

Response表：

Question ID     Response day
1               01-04-15
3               02-04-15
4               03-04-15

我希望输出结果为：

Question ID  Response day
1            01-04-15
2            null
3            02-04-15
4            03-04-15

我正在尝试使用以下查询，并且当有响应时我正在获取问题ID。谁知道我哪里出错？

select questionID, responseday 
from questions
join response
where question.question.ID = response.question.ID;

通过此查询，我得到了这些结果：

Question  ID    Response day
1               01-04-15
3               02-04-15
4               03-04-15

Answer 1

一种方法是完全外连接：

select coalesce(q.questionid, r.questionid) as questionid,
       r.responseday
from questions q full outer join
     responses r
     on q.questionid = r.questionid;

Answer 2

使用左连接

delay

Answer 3

根据您的架构，简单的LEFT JOIN对您的模型就足够了。

SELECT     q.Question_ID, 
           r.Response_Day
FROM       Question AS "q"
           LEFT JOIN Response AS "r"
                ON r.Question_ID = q.Question_ID;

JOIN或INNER JOIN 仅会返回ALL属性匹配的两个表中的结果集。由于响应表中不存在ID为Question的{{1}}记录，因此SQL将排除此数据。

要考虑2，您必须NULLs，请在此处查看sqlfiddle： SQL Fiddle

另外，请看一下解释所有LEFT JOIN的图形模型： Visual Representation of SQL Joins

Answer 4

FULL outer JOIN is sufficient or the output required.

SELECT NVL(a.id,b.id),
  b.nm
FROM
  (SELECT 1 id,1 nm FROM dual
  UNION ALL
  SELECT 2 id,2 nm FROM dual
  UNION ALL
  SELECT 3 id,3 nm FROM dual
  )a
FULL OUTER JOIN
  (SELECT 1 id,'01-04-15' nm FROM dual
  UNION
  SELECT 3 id,'02-04-15' nm FROM dual
  UNION ALL
  SELECT 4 id,'03-04-15' nm FROM dual
  )b
ON a.id = b.id;


---------------------------------OUTPUT -----------------------------------

ID  NM
1   01-04-15
3   02-04-15
4   03-04-15
2   NULL
----------------------------------OUTPUT-----------------------------------

Answer 5

select questionID
,      responseday 
from   questions
join   response
   on  question.question.ID = response.question.ID;

如何在SQL中选择2个表之间的所有值？

5 个答案: