Mysql SQLite内部联接限制1
我有两个表Mysql SQLite内部联接限制1,mysql,sql,sqlite,Mysql,Sql,Sqlite,我有两个表objectTable和photo\u table。下面是来自objectTable ID TEXT 1 Kaunas 2 Vilnius 3 Palanga 4 Prienai OBJECT_ID PHOTO_ID NAME 1 7 tets7.jpg 1 8 tets8.jpg 1 9 tets9.jpg 1 10 tets10.jpg 1
objectTable
和photo\u table
。下面是来自objectTable
ID TEXT
1 Kaunas
2 Vilnius
3 Palanga
4 Prienai
OBJECT_ID PHOTO_ID NAME
1 7 tets7.jpg
1 8 tets8.jpg
1 9 tets9.jpg
1 10 tets10.jpg
1 11 tets11.jpg
2 3 tets3.jpg
2 2 tets2.jpg
3 1 tets1.jpg
3 5 tets5.jpg
4 6 tets6.jpg
4 7 tets7.jpg
4 8 tets8.jpg
下面是来自photo\u表的数据
ID TEXT
1 Kaunas
2 Vilnius
3 Palanga
4 Prienai
OBJECT_ID PHOTO_ID NAME
1 7 tets7.jpg
1 8 tets8.jpg
1 9 tets9.jpg
1 10 tets10.jpg
1 11 tets11.jpg
2 3 tets3.jpg
2 2 tets2.jpg
3 1 tets1.jpg
3 5 tets5.jpg
4 6 tets6.jpg
4 7 tets7.jpg
4 8 tets8.jpg
正如你所看到的,一个物体可以有很多图案。我需要得到evety对象的第一张图片(我的输出应该是)
我的问题是:
select *
from objectTable
inner join photo_table
on photo_table.OBJECT_ID = (select OBJECT_ID
from photo_table
where photo_table.OBJECT_ID = objectTable.ID
order by photo_table.OBJECT_ID desc
limit 1).
然而,我试图用将近3个小时来解释为什么这个查询不起作用。我错过了什么?我的逻辑正确吗?请尝试以下方法:
SELECT t1.*, t3.NAME
FROM objectTable AS t1
INNER JOIN (
SELECT OBJECT_ID, MIN(PHOTO_ID) AS PHOTO_ID
FROM photo_table
GROUP BY OBJECT_ID
) t2 ON t1.ID = t2.OBJECT_ID
INNER JOIN photo_table AS t3 ON t3.OBJECT_ID = t2.OBJECT_ID AND
t3.PHOTO_ID = t2.PHOTO_ID
诀窍是使用派生表来选择每个对象ID
的照片ID
值。此值用于对photo\u表的附加联接,以便选择所需的名称
值。请尝试以下方法:
SELECT t1.*, t3.NAME
FROM objectTable AS t1
INNER JOIN (
SELECT OBJECT_ID, MIN(PHOTO_ID) AS PHOTO_ID
FROM photo_table
GROUP BY OBJECT_ID
) t2 ON t1.ID = t2.OBJECT_ID
INNER JOIN photo_table AS t3 ON t3.OBJECT_ID = t2.OBJECT_ID AND
t3.PHOTO_ID = t2.PHOTO_ID
诀窍是使用派生表来选择每个对象ID
的照片ID
值。此值用于photo_table
的附加联接中,以便选择所需的名称
值。根据您的代码,我将更改ASC的描述和订购它的ID列,以获得ID最低的照片
select *
from objectTable
inner join photo_table
on photo_table.OBJECT_ID = (select OBJECT_ID
from photo_table
where photo_table.OBJECT_ID = objectTable.ID
order by photo_table.PHOTO_ID ASC
limit 1).
按照你的代码,我将更改ASC的DESC和订购它的ID列,以获得ID最低的照片
select *
from objectTable
inner join photo_table
on photo_table.OBJECT_ID = (select OBJECT_ID
from photo_table
where photo_table.OBJECT_ID = objectTable.ID
order by photo_table.PHOTO_ID ASC
limit 1).
您的示例输出没有意义。您说您希望获得每个对象的第一张图片,但图片“第一”的原因是什么?对于示例输出中的第二个结果,照片的顺序必须与其他按升序排序的照片的顺序相反。您确定“tets3.jpg”不应该是“tets2.jpg”吗?您的示例输出没有意义。您说您希望获得每个对象的第一张图片,但图片“第一”的原因是什么?对于示例输出中的第二个结果,照片的顺序必须与其他按升序排序的照片的顺序相反。你确定“tets3.jpg”不应该是“tets2.jpg”吗?