Question

是否可以将这两个左连接合并为一个？

我想不出任何方式

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()获取同一查询中每个某个字段的最大字段数。

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

请试试这个..

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

试试这个，但没有数据和输出的样本我不能保证它能正常工作，它只是在猜测。

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

将同一个表上的两个左连接合并为一个

3 个答案: