如何使用一个MySQL查询选择所有带有标签的文章和所有文章的标签？

Question

我有3个表:文章(id，标题，内容)，标签(id，标签)和模块(id，iditem，idtag，tags2all )。我希望选择具有特定标签的所有文章，但在结果列表中，我还希望能够显示每篇文章的标签。

目前，我正在使用这个查询来显示文章列表：

SELECT GROUP_CONCAT(t.tag SEPARATOR ', ') AS tags,a.* FROM articles AS a LEFT JOIN tags2all AS ta ON ta.iditem=a.id AND ta.module='articles' JOIN tags AS t ON ta.idtag=t.id GROUP BY a.id HAVING a.title IS NOT NULL

它似乎工作得相当好，但我似乎不知道应该向查询添加什么内容，以便只显示具有特定标签的文章。

如果我添加WHERE t.id=3，它会选择正确的文章，但标记列表将只包含该标记。

Answer 1

这对我来说似乎没什么问题：

select a.*
from
(
SELECT GROUP_CONCAT(t.tag SEPARATOR ', ') AS tags,a.id,a.title,a.content
FROM articles AS a LEFT JOIN tags2all AS ta ON ta.iditem=a.id 
AND ta.module='articles' JOIN tags AS t ON ta.idtag=t.id 
GROUP BY a.id HAVING a.title IS NOT NULL
) a inner join tags2all t2a on t2a.iditem = a.id
inner join tags t on t.id = t2a.idtag
where t.id = 3;

下面是我使用的DDL和数据：

create table articles (id int unsigned not null primary key, title varchar(50), content varchar(50));

create table tags (id int unsigned not null primary key, tag varchar(50));

create table tags2all (id int unsigned not null primary key, iditem int unsigned not null, idtag int unsigned not null, module varchar(50));

insert into articles values (1,"Article1","Some content");
insert into articles values (2,"Article2","Some content");
insert into articles values (3,"Article3","Some content");

insert into tags values (1,"Tag1");
insert into tags values (2,"Tag2");
insert into tags values (3,"Tag3");
insert into tags values (4,"Tag4");
insert into tags values (5,"Tag5");
insert into tags values (6,"Tag6");
insert into tags values (7,"Tag7");

insert into tags2all (id,iditem,idtag,module) values (1,1,1,"articles");
insert into tags2all (id,iditem,idtag,module) values (2,1,2,"articles");
insert into tags2all (id,iditem,idtag,module) values (3,1,3,"articles");
insert into tags2all (id,iditem,idtag,module) values (4,2,3,"articles");
insert into tags2all (id,iditem,idtag,module) values (5,2,4,"articles");
insert into tags2all (id,iditem,idtag,module) values (6,2,5,"articles");
insert into tags2all (id,iditem,idtag,module) values (7,3,3,"articles");
insert into tags2all (id,iditem,idtag,module) values (8,3,4,"articles");
insert into tags2all (id,iditem,idtag,module) values (9,3,7,"articles");

Answer 2

我不确定，但让我们试一下

SELECT GROUP_CONCAT(t.tag SEPARATOR ', ') AS tags,a.* FROM articles AS a 
LEFT JOIN tags2all AS ta ON ta.iditem=a.id AND ta.module='articles' 
JOIN tags AS t ON ta.idtag=t.id 
JOIN tags AS t1 ON ta1.idtag=t.id
GROUP BY a.id HAVING a.title IS NOT NULL