在MSSQL中,我有两个具有一对多关系的表。
表:
tb_Products:
ID
ProductName
tb_Images:
ProductID
MidPath
在存储过程中,显示带有图像的产品(也显示空记录),如果tb_Images中有多个productID,则显示单个记录。
我可以通过此查询来完成这项工作:
declare @rowIndexToFetch int
set @rowIndexToFetch=0
select p.ID,p.ProductName,p.CategoryID,c.ParentId,
pi.MidPath
from tb_Products p
join tb_Categories c
on p.CategoryID=c.ID
left outer join tb_Images pi
on pi.ProductID=p.ID
where c.ID=3 or c.ParentId=3
order by pi.ID desc
offset @rowIndexToFetch rows
fetch next 1 rows only
但是,如果我使用offset和fetch,我不再能从tb_Images中检索NULL记录。左外连接不再起作用。
示例记录返回没有offset-fetch:
ID ProductName CategoryID ParentId MidPath
154 Chef Ceket 33 3 /cdn/www.sample.com/x
154 Chef Ceket 33 3 /cdn/www.sample.com/y
154 Chef Ceket 33 3 /cdn/www.sample.com/z
1 Eldiven 3 3 NULL
使用offset-fetch:
ID ProductName CategoryID ParentId MidPath
154 Chef Ceket 33 3 /cdn/www.sample.com/x
预计会回归:
ID ProductName CategoryID ParentId MidPath
154 Chef Ceket 33 3 /cdn/www.sample.com/x
1 Eldiven 3 3 NULL
问题是,当我使用offset-fetch语句时,我无法检索空记录。我怎样才能解决这个问题?
根据你的评论,我认为你误解了OFFSET FETCH构造的行为。再看看手册。
如果您想获得上述结果,可以使用此类查询
WITH query AS (
SELECT
p.ID,
p.ProductName,
p.CategoryID,
c.ParentId,
pi.MidPath,
rn = ROW_NUMBER() OVER( PARTITION BY p.ID ORDER BY pi.MidPath )-- in your code ORDER set by pi.ID but there's no evidence it exists
FROM tb_Products p
JOIN tb_Categories c ON p.CategoryID = c.ID
LEFT JOIN tb_Images pi ON pi.ProductID = p.ID
WHERE c.ID = 3 or c.ParentId = 3
)
SELECT ID, ProductName, CategoryID, ParentId, MidPath
FROM query
WHERE rn = 1
select distinct p.ID,p.ProductName,p.CategoryID,c.ParentId,
pi.MidPath
from tb_Products p
join tb_Categories c
on p.CategoryID=c.ID
left outer join tb_Images pi
on pi.ProductID=p.ID
where c.ID=3 or c.ParentId=3
where c.ID=3 or c.ParentId=3
试试这个代码,在productImage中最大。每个productID的值为1。
WITH productImage
AS ( SELECT MAX(pi.ID) AS ID
, pi.ProductID
FROM tb_Images pi
GROUP BY pi.ProductID
)
SELECT p.ID
, p.ProductName
, p.CategoryID
, c.ParentId
, pi.MidPath
FROM tb_Products p
JOIN tb_Categories c ON p.CategoryID = c.ID
LEFT OUTER JOIN productImage ON productImage.ProductID = p.ID
LEFT OUTER JOIN tb_Images pi ON pi.ID = productImage.ID
WHERE c.ID = 3
OR c.ParentId = 3;