根据联合中使用的列获取正确的记录

Question

此 select 在包中用作 left outer join：

 SELECT * (SELECT db1.id, db2.value, db1.discount, 2 AS attr_number FROM database1 db1
      JOIN database2 db2 ON db2.db1_id = db1.id
    WHERE db2.value = 1
    UNION
    SELECT db1.id, db4.value, db1.discount, 1 AS attr_number FROM database1 db1
      JOIN database4 db4 ON db4.db1_id = db1.id
    WHERE db4.value = 1) WHERE id = 225

他 return给我发了这个记录：

|ID           |VALUE             |DISCOUNT          |ATTR_NUMBER       |
|-------------|------------------|------------------|------------------|
|225          |1                 |50                |2                 |
|225          |1                 |50                |2                 |
|225          |1                 |40                |1                 |
|225          |1                 |40                |1                 |
|225          |1                 |40                |1                 |

所以我需要考虑 attr_number 行并根据该字段获取记录。

如您所见，attr_number 行值只能是 1 或 2。

根据这个例子，记录存在两个值，在这种情况下我们只需要 return attr_number = 1（因为它存在），所以这是一个他应该 [=38] 的例子=]:

|ID           |VALUE             |DISCOUNT          |ATTR_NUMBER       |
|-------------|------------------|------------------|------------------|
|225          |1                 |40                |1                 |
|225          |1                 |40                |1                 |
|225          |1                 |40                |1                 |

如您所见，他 "removed" 记录 attr_number = 2 和 returning 仅在 1 的位置。

在其他情况下，如果select不return记录where attr_number = 1，他return所有其他记录，在这种情况下它会是attr_number = 2。这是他在这种情况下应该 return 的示例：

|ID           |VALUE             |DISCOUNT          |ATTR_NUMBER       |
|-------------|------------------|------------------|------------------|
|225          |1                 |50                |2                 |
|225          |1                 |50                |2                 |

希望我的解释足够清楚。

Answer 1

创建 2 个 CTE，每个联合查询一个，然后使用 NOT EXISTS：

WITH 
  cte1 AS (
    SELECT db1.id, db4.value, db1.discount, 1 AS attr_number 
    FROM database1 db1 JOIN database4 db4 
    ON db4.db1_id = db1.id
    WHERE id = 225 AND value = 1
  ),
  cte2 AS (
    SELECT db1.id, db2.value, db1.discount, 2 AS attr_number 
    FROM database1 db1 JOIN database2 db2 
    ON db2.db1_id = db1.id
    WHERE id = 225 db2.value = 1
  )
SELECT * FROM cte1
UNION ALL
SELECT * FROM cte2
WHERE NOT EXISTS (SELECT 1 FROM cte1 WHERE attr_number = 1)

Answer 2

您可以使用 RANK 对结果进行排名，只保留最好的行（即 attr_number 较低的行）。

select db1.id, 1 as value, db1.discount, dbx.attr_number
from database1 db1
join
(
  select db1_id, attr_number, rank() over (order by attr_number) as rn
  from
  (
    select db1_id, 2 as attr_number from database2 db2 where value = 1
    union all
    select db1_id, 1 as attr_number from database4 db4 where value = 1
  )
) dbx on dbx.db1_id = db1.id and dbx.rn = 1
where db1.id = 225;

根据联合中使用的列获取正确的记录

Get correct records based on column from union which are used in join

sql

oracle

oracle10g