Question

我需要从键值对表中检索具有不同键的3个值。

我的数据库架构如下。我需要通过获取E_SUBID然后使用E_SUBID连接table2，从table1到达table3。一旦table1和table2加入，我需要从table2获取E_CID以将其与table2 E_CID连接以获得“Attr_Value”以保持E_CID作为标准。

表1

------------------------
|E_SUBID| B_LocationID |
|1        100          |
|2        101          |
|3        102          |

表2

-----------------
|E_CID | E_SUBID|
|10       1     |
|11       2     |
|12       3     |

表3

--------------------------------- 
|E_CID | Attr_name | Attr_Value  |
|10       Product    Samsung     |
|10       Model      Smartphone  |
|10       usage      daily       |
|11       Product    Apple       |
|11       Model      Ipad        |
|11       usage      everyday    |
|12       Model      smartwatch  |

我已成功加入table1，table2和table3，但我无法获得所需的输出，如下所示

输出

 |Product | Model      | Usage    |
  Samsung   Smartphone   daily  
  Apple     Ipad         everyday
  null      smartwatch    null

将table1，table2和table3连接起来的查询如下

select distinct t3.Attr_value as Product
from table1 t1, table2 t2, table3 t3
where t1.E_SUBID = t2.E_SUBID and
      t2.E_CID = t3.E_CID  and
      t3.Attr_name=?????
 order by Product;

感谢您的时间。

Answer 1

尝试如下...基本上你试图将行转置到table3中的列。

Select Product, "Model", Usage
From
(
Select 
t1.E_SUBID,
t2.E_CID,
Max(Case when T3.Attr_name = 'Product' Then T3.Attr_Value else null end) Product,
max(Case when T3.Attr_name = 'Model' Then T3.Attr_Value else null end) Model,
max(Case when T3.Attr_name = 'Usage' Then T3.Attr_Value else null end) Usage
From Table1 t1,
     Table2 t2,
     Table3 t3
Where 
    t1.E_SUBID = t2.E_SUBID
and t2.E_CID = t3.E_CID
group by t1.t1.E_SUBID,t2.E_CID
);

Answer 2

在这种情况下，您可以根据需要随时加入table3您希望展示的每个属性name：

select 
  p.attr_value product,
  m.attr_value "model", -- Quotes to escape reserved word
  u.attr_value usage
from table1 t1
join table2 t2 on t1.e_subid = t2.e_subid
left outer join table3 p on t2.e_cid = p.e_cid and p.attr_name = 'Product'
left outer join table3 m on t2.e_cid = m.e_cid and m.attr_name = 'Model'
left outer join table3 u on t2.e_cid = u.e_cid and u.attr_name = 'Usage'
order by 1;

修改根据评论，通过使table3可选（outer join），查询应返回所有行以及是否已定义Model或Usage或Product。

从Oracle数据库键值对中检索

2 个答案: