1

我有三张桌子：

CREATE TABLE category (id integer, parent_id integer);
CREATE TABLE category_name (id integer, name (varchar(20), language_id);
CREATE TABLE language (language_id integer, language_name);

我可以通过以下语句获得子-父母-祖父母关系：

SELECT c.id, c.parent_id, p.parent_id 
FROM category AS p, category AS c 
WHERE p.id = c.parent_id AND p.parent_id IS NOT NULL;

但是我还需要从表 category_name 中获取孩子、父母和祖父母的名字，其中 language_id = 3

在没有子-父母-祖父母关系的情况下，获取名称的查询将是这样的：

SELECT c.id, n.name
FROM category c
LEFT JOIN category_name n ON c.id = n.id AND language_ID = 3

但是如何将这两个语句合并为一个，以便我实际上得到三个名称列呢？也就是说，每一行都应该有自己的 ID 和名称，它的父母和它的祖父母（如果后者存在的话）

如何继续进行此组合查询？

以下是表格和一些示例数据：

CREATE TABLE category (id integer, parent_id integer);
INSERT INTO category VALUES (1,null);
INSERT INTO category VALUES (2,null);
INSERT INTO category VALUES (3,1);
INSERT INTO category VALUES (4,2);
INSERT INTO category VALUES (5,2);
INSERT INTO category VALUES (6,4);
INSERT INTO category VALUES (7,2);
INSERT INTO category VALUES (8,7);
INSERT INTO category VALUES (9,7);
INSERT INTO category VALUES (10,7);
INSERT INTO category VALUES (11,3);

CREATE TABLE category_name (id integer, name varchar(20), language_id integer);
INSERT INTO category_name VALUES (1, 'CDs', 3);
INSERT INTO category_name VALUES (2, 'Books', 3);
INSERT INTO category_name VALUES (3, 'Music', 3);
INSERT INTO category_name VALUES (4, 'Novels', 3);
INSERT INTO category_name VALUES (5, 'Childrens books', 3);
INSERT INTO category_name VALUES (6, 'European', 3);
INSERT INTO category_name VALUES (7, 'Science', 3);
INSERT INTO category_name VALUES (8, 'Math', 3);
INSERT INTO category_name VALUES (9, 'Informatics', 3);
INSERT INTO category_name VALUES (10, 'Physics', 3);
INSERT INTO category_name VALUES (11, 'Classic', 3);
INSERT INTO category_name VALUES (1, 'CDs', 4);
INSERT INTO category_name VALUES (2, 'Livres', 4);
INSERT INTO category_name VALUES (3, 'Musique', 4);
INSERT INTO category_name VALUES (4, 'Romans', 4);

CREATE TABLE language (language_id integer, language_name varchar(15));
INSERT INTO language (3, 'English');
INSERT INTO language (4, 'French');

这是我想获取一些样本的方式（对于 c.id = 5 和 8）：

c.id | c.parent_id | p.parent_id | nameChild          | nameParent | nameGrandparent
5    | 2           | null        | 'Children's books' | 'Books'    | null
8    | 7           | 2           | 'Math'             | 'Science'  | 'Books'

我尝试了以下代码，但它给出了错误代码：1054。“on 子句”中的未知列“p.parent_id”

SELECT c.id, c.parent_id, p.parent_id, nc.name, np.name, ng.name 
FROM category1 AS p, category1 AS c 
LEFT JOIN category_name1 AS nc ON c.id = nc.id AND nc.language_id = 3
LEFT JOIN category_name1 AS np ON c.parent_id = np.id AND np.language_id = 3
LEFT JOIN category_name1 AS ng ON p.parent_id = ng.id AND ng.language_id = 3 AND p.parent_id IS NOT NULL
WHERE p.id = c.parent_id AND p.parent_id IS NOT NULL;

说出孩子和父母的名字我没有问题，但祖父母的名字似乎超出了我的掌握:(

下面是代码工作！

SELECT x.id, x.pid, x.gpid, 
nc.name childName, np.name parentName, ng.name gpName 
FROM 
(SELECT  c.id , c.parent_id AS pid, p.parent_id AS gpid
FROM
category AS c
LEFT JOIN category AS p ON p.id = c.parent_id
) x


LEFT JOIN category_name AS nc ON x.id = nc.id AND nc.language_id = 3
LEFT JOIN category_name AS np ON x.pid = np.id AND np.language_id = 3
LEFT JOIN category_name AS ng ON x.gpid = ng.id AND ng.language_id = 3;
4

2 回答 2

1

请尝试一下并发表评论。查询和结果都基于我自己的样本。

此查询选择language name, category namewith language id =something, group by parent id。

询问：

select l.language_name, cl.name, c.parent_id
from category c
left join 
category_name cl
on c.parent_id = cl.id
inner join 
language l
on cl.language_id = l.language_id
where l.language_id = 30
group by c.parent_id
;

结果：

LANGUAGE_NAME   NAME    PARENT_ID
eng             cat4c   4

以下查询category name为parent id每个language.

询问：

select l.language_name, cl.name, c.parent_id
from language l
left join 
category_name cl
on cl.language_id = l.language_id
left join 
category c
on c.parent_id = cl.id
group by l.language_id
;

结果：

LANGUAGE_NAME   NAME    PARENT_ID
jpn             cat1    (null)
kor             cat3    3
eng             cat4    4

使用示例数据和预期结果根据 OP 的更新问题进行编辑

询问：

select x.id, x.pid, x.gpid, 
cl.name ccat, cl2.name pcat, cl3.name gpcat
from
(SELECT c.id , c.parent_id as pid, 
p.parent_id gpid
FROM category AS c
left join category AS p 
on p.id = c.parent_id 
WHERE c.id in (5, 8)
) x
left join 
category_name cl
on cl.id = x.id
left join category_name cl2
on cl2.id = x.pid
left join category_name cl3
on cl3.id = x.gpid
group by x.id
;

结果：

ID  PID     GPID    CCAT        PCAT    GPCAT
5   2       (null)  Children    Books   (null)
8   7       2       Math        Science Books
于 2013-01-08T00:01:25.687 回答
0

像这样的东西应该工作：

SELECT 
c.id AS childId, cname.name AS childName,
p.id AS parentId, pname.name AS parentName,
g.id AS grandparentId, gname.name AS grandparentName
FROM category p
INNER JOIN category c ON (p.id = c.parent_id)
LEFT JOIN category g ON (p.parent_id = g.id)
LEFT JOIN category_name cname ON (c.id = cname.id AND cname.language_ID = 3)
LEFT JOIN category_name pname ON (p.id = pname.id AND pname.language_ID = 3)
LEFT JOIN category_name gname ON (g.id = gname.id AND gname.language_ID = 3)
WHERE p.parent_id IS NOT NULL;

我觉得应该有一种更简洁的方法来做到这一点，但目前看不到。

于 2013-01-08T02:03:05.697 回答