將同一個表上的兩個左連接合併爲一個

Question

是否可以將這兩個左連接合併爲一個？

我想不出任何辦法

select left1.field1, 
     left2.field2 
from masterTable left join (
    select somefield, 
     field1, 
     row_number() over (partition by somefield orderby otherfield) as rowNum 
    from childTable 
    inner join masterTable 
     on masterTable.somefield = childTable.somefield 
    ) as left1 
     on masterTable.somefield = left1.somefield 
       AND left1.rownum =1 
left join (
    select somefield, 
      max(field2) as field2 
    from childTable 
    inner join masterTable 
     on masterTable.somefield = childTable.somefield 
    where field3 = 1 
    group by somefield 
    ) as left2 
     on masterTable.somefield = left2.somefield 

Answer 1

您可以使用max() over()，讓每somefield場2的最大值在相同的查詢。

select left1.field1, 
     left1.field2 
from masterTable 
left join 
(select 
somefield,field1 
,row_number() over (partition by somefield orderby otherfield) as rowNum 
,max(field2) over(partition by somefield) as field2 
from childTable 
inner join masterTable on masterTable.somefield = childTable.somefield) as left1 
ON masterTable.somefield = left1.somefield 
AND left1.rownum =1 AND field3 = 1 

Answer 2

請試試這個..

select left1.field1, 
     left1.field2 
from masterTable 
left join 
(select 
somefield,field1 
,row_number() over (partition by somefield orderby otherfield) as rowNum 
,max(field2) over(partition by somefield) as field2 
from childTable 
inner join masterTable on masterTable.somefield = childTable.somefield 
group by somefield,field1 
,row_number() over (partition by somefield orderby otherfield) 

) 
as left1 
ON masterTable.somefield = left1.somefield 
AND left1.rownum =1 AND field3 = 1 

Answer 3

試試這個，但沒有數據和輸出的樣本，我不能保證它會正常工作，這只是猜測。

SELECT field1, 
     MAX(field2) AS field2 
FROM (
    SELECT ct.field1, 
      ct1.field2, 
      ROW_NUMBER() OVER (PARTITION BY ct.somefield ORDER BY ct.otherfield) as rn 
    FROM masterTable mt 
    INNER JOIN childTable ct 
     ON mt.somefield = ct.somefield 
    LEFT JOIN childTable ct1 
     ON mt.somefield = ct1.somefield AND ct1.field3 = 1 
    ) as t 
WHERE rn = 1 
GROUP BY ct.field1