Question

我有两个表，我无法改变，我试图从两个表中查询和组合一些数据。我理想的做法是在FieldTime2为0时组合省略行，当同一FieldID有两个以上的结果时。如果FieldTime2为0并且只有一个结果，那么我希望显示该行。

你可以计算表2中的FieldID并在count大于1时指定一个数字，或类似的东西？

表1

ID  FieldID  FieldTime
------------------------
 1   A        10
 2   B        15
 3   C        20

表2

 ID  FieldID  FieldTime2
------------------------
 1   A        0
 2   A        15
 3   B        0
 4   C        10

期望的输出：

FieldID  FieldTime  FieldTime2
------------------------------
  A      10         15
  B      15         0
  C      20         10

我的输出：

FieldID  FieldTime  FieldTime2
------------------------------
      A      10         0
      A      10         15
      B      15         0
      C      20         10

CODE：

SELECT
    m.FieldID, 
    m.FieldTime,
    n.FieldTime2,

from Table1 m
   Join Table2 n
       ON m.FieldID = n.FieldID

Where n.FieldTime > 0

Answer 1

最简单的解决方案是使用LEFT JOIN查询，如下所示：

SELECT
    m.FieldID, 
    m.FieldTime,
    COALESCE(n.FieldTime2, 0) as FieldTime2,

from Table1 m
  left Join Table2 n
       ON m.FieldID = n.FieldID and n.FieldTime2 > 0

Where n.FieldTime > 0

如果Table2中有多个非零记录且只需要一个，那么查询将会有点复杂：

with n as (
select *,
ROW_NUMBER() OVER(PARTITION BY FieldID ORDER BY FieldTime2 DESC) rn
from Table2
)
SELECT
    m.FieldID, 
    m.FieldTime,
    COALESCE(n.FieldTime2, 0) as FieldTime2,

from Table1 m
  LEFT Join n
       ON m.FieldID = n.FieldID and n.rn = 1

Where n.FieldTime > 0

Answer 2

根据您的数据样本，并假设只有FieldTime只有value > 0，您只需使用MAX()来解决问题：

SELECT
    m.FieldID, 
    m.FieldTime,
    MAX(n.FieldTime2),
FROM Table1 m
JOIN Table2 n ON m.FieldID = n.FieldID
WHERE n.FieldTime > 0
GROUP BY m.FieldID, m.FieldTime

当然，如果可能有多个FieldTime记录包含value > 0，此解决方案将无法呈现正确的输出，在这种情况下，您可以使用UNION来解决问题：

--cases with one record:
SELECT
    m.FieldID, 
    m.FieldTime,
    n.FieldTime2
FROM Table1 m
JOIN Table2 n ON m.FieldID = n.FieldID
Where m.FieldID in
(
   SELECT FieldID 
   FROM Table2
   HAVING COUNT(FieldID) = 1 -- only one record exists
)
UNION 
--cases with multiple records
SELECT
    m.FieldID, 
    m.FieldTime,
    n.FieldTime2
FROM Table1 m
JOIN Table2 n ON m.FieldID = n.FieldID
Where m.FieldID not in --make sure we select the rest of the records
(
   SELECT FieldID 
   FROM Table2
   HAVING COUNT(FieldID) = 1 
) AND n.FieldTime2 > 0 -- make sure to exclude the 0 records.

请注意，这未经过测试，因此请考虑拼写错误，性能不佳或错误。：）

在连接两个表时将结果组合在第二个表中

2 个答案: