PostgreSQL JOIN 来自 3 个表的数据
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PostgreSQL JOIN data from 3 tables
提问by John Cleary
I'm new to PostgreSQL and trying to get a query written. I'm pretty sure it's easy for someone who knows what they are doing - I just don't! :)
我是 PostgreSQL 的新手，正在尝试编写查询。我很确定这对于知道自己在做什么的人来说很容易——我就是不知道！:)
Basically I have three tables. In the first, I store details about patients. In the second, I store a reference to each image of them. In the third, I store the link to the file path for the image. I didn't design the database, so I'm not sure why the image files table is separated, but it is.
基本上我有三张桌子。首先，我存储有关患者的详细信息。在第二个中，我存储对它们的每个图像的引用。在第三个中，我存储指向图像文件路径的链接。我没有设计数据库，所以我不确定为什么图像文件表是分开的，但确实如此。
What I want to be able to do is select data from the first table, joining in data from a second then third table so I end up with the name & file path in the result.
我想要做的是从第一个表中选择数据，加入第二个然后第三个表中的数据，这样我最终会在结果中得到名称和文件路径。
So the basic structure is:
所以基本结构是：
Table 1:
person_id | name
Table 2:
person_id | image_id
Table 3:
image_id | `path filename`
What I want to do is in one query, grab the person's 'name' and the image 'path filename'.
我想要做的是在一个查询中，获取此人的“姓名”和图像“路径文件名”。
I'm happy with a "template" style answer with the join I need. I don't need it to be written in actual code. (i.e. I'm thinking you can just write me an answer that says SELECT table1.name, table3.pathfilename FROM JOIN ... etc...).
我对带有我需要的连接的“模板”样式的答案感到满意。我不需要用实际代码编写它。（即我想你可以给我写一个答案，上面写着SELECT table1.name, table3.pathfilename FROM JOIN ... etc...）。
回答by ozczecho
Something like:
就像是：
select t1.name, t2.image_id, t3.path
from table1 t1 inner join table2 t2 on t1.person_id = t2.person_id
inner join table3 t3 on t2.image_id=t3.image_id
回答by Daniel Frey
Maybe the following is what you are looking for:
也许以下是您正在寻找的内容：
SELECT name, pathfilename
FROM table1
NATURAL JOIN table2
NATURAL JOIN table3
WHERE name = 'John';
