我在 MS SQL 中工作,但除了表变量之外,我没有看到任何特定于 MS 的东西。因此,如果您将其更改为现有表,它也应该在 MySQL 上运行。(我不确定,但我猜 MySQL 应该有 EXCEPT 操作。)
-- sample data start
declare @place as table (plid int, plname nvarchar(100))
declare @photo as table (phid int, phname nvarchar(100), plid int, primary_pic nvarchar(1))
insert into @place values (1, 'aaa')
insert into @place values (2, 'bbb')
insert into @photo values (1, 'aaa_1.jpg', 1, '')
insert into @photo values (2, 'aaa_2.jpg', 1, 'X')
insert into @photo values (3, 'aaa_3.jpg', 1, '')
insert into @photo values (4, 'aaa_4.jpg', 1, '')
insert into @photo values (5, 'bbb_1.jpg', 2, '')
insert into @photo values (6, 'bbb_2.jpg', 2, '')
insert into @photo values (7, 'bbb_3.jpg', 2, '')
insert into @photo values (8, 'bbb_4.jpg', 2, '')
-- sample data end
-- note: @place and @photo are table variables in MS SQL
select p.*, ph2.*
from @place p inner join @photo ph2 on p.plid = ph2.plid
inner join (
select ph.plid, ph.primary_pic, min(ph.phid) phid
from @photo ph inner join
(select distinct plid from @photo where primary_pic <> 'X'
except
select distinct plid from @photo where primary_pic = 'X') hasnoprimary
on hasnoprimary.plid = ph.plid
group by ph.plid, ph.primary_pic
union
select ph.plid, ph.primary_pic, min(ph.phid) phid
from @photo ph inner join
(select distinct plid from @photo where primary_pic = 'X') hasprimary
on hasprimary.plid = ph.plid
where primary_pic = 'X'
group by ph.plid, ph.primary_pic
) trickypart on trickypart.phid = ph2.phid
方法:(1)获取两个地点ID列表。一张有主照片,另一张没有(这是我使用的地方除外)。(2) 将照片表分别连接到它们两者以获取照片ID。对于第一个列表,它是用 X 标记的,对于第二个,它是所有照片 ID 中的最小值。(3) 将两者结合起来。(4)加入它回的地方和照片。
在 MS SQL 中,它的工作原理是为上面的示例数据提供以下内容:
plid plname phid phname plid primary_pic
----------- -------------- ----------- -------------- ----------- -----------
1 aaa 2 aaa_2.jpg 1 X
2 bbb 5 bbb_1.jpg 2