MySQL 在查询中生成注释子列表

Question

我有一个包含 3 个表问题、答案、评论的数据库，它按预期工作，每个问题可以有多个答案，每个答案可以有多个评论

create table Question(
    questionId int primary key auto_increment,
    title varchar(34) not null,
    content TEXT not null
);

create table Answer(
    answerId int primary key auto_increment,
    questionId int not null,
    content TEXT not null
);

create table Comment(
    commentId int primary key auto_increment,
    answerId int,
    questionId int,
    content TEXT not null
);

insert into Question(title, content) values('Testing Question','Testing Question');

insert into Answer(questionId, content) values(1,'Testing Answer 1');
insert into Answer(questionId, content) values(1,'Testing Answer 2');

insert into Comment(answerId, questionId, content) values(1, 1,'Testing Comment 1 to Answer 1');
insert into Comment(answerId, questionId, content) values(1, 1,'Testing Comment 2 to Answer 1');
insert into Comment(answerId, questionId, content) values(2, 1,'Testing Comment 1 to Answer 2');
insert into Comment(answerId, questionId, content) values(2, 1,'Testing Comment 2 to Answer 2');

我希望当我查询一个答案及其 cmets 时，我会在一个 List 中获得这些 cmets，例如：

[
{ answerId: 1, answerContent: 'Answer Content', comments[...]},
{ answerId: 2, answerContent: 'Answer Content', comments[...]}
]

这可能吗？我曾尝试使用此查询：

select * from Answer inner join Comment on Comment.answerId = Answer.answerId where Comment.questionId = 1;

显然它给了我这个：

[
    {
        "answerId" : 1,
        "questionId" : 1,
        "content" : "Testing Answer 1",
        "commentId" : 1,
        "answerId" : 1,
        "questionId" : 1,
        "content" : "Testing Comment 1 to Answer 1"
    },
    {
        "answerId" : 1,
        "questionId" : 1,
        "content" : "Testing Answer 1",
        "commentId" : 2,
        "answerId" : 1,
        "questionId" : 1,
        "content" : "Testing Comment 2 to Answer 1"
    },
    {
        "answerId" : 2,
        "questionId" : 1,
        "content" : "Testing Answer 2",
        "commentId" : 3,
        "answerId" : 2,
        "questionId" : 1,
        "content" : "Testing Comment 1 to Answer 2"
    },
    {
        "answerId" : 2,
        "questionId" : 1,
        "content" : "Testing Answer 2",
        "commentId" : 4,
        "answerId" : 2,
        "questionId" : 1,
        "content" : "Testing Comment 2 to Answer 2"
    }
]

我也尝试过在上一个查询中使用 group by，如下所示：

select * from Answer inner join Comment on Comment.answerId = Answer.answerId where Comment.questionId = 1 group by Comment.questionId;

它还给了我这个：

[
    {
        "answerId" : 1,
        "questionId" : 1,
        "content" : "Testing Answer 1",
        "commentId" : 1,
        "answerId" : 1,
        "questionId" : 1,
        "content" : "Testing Comment 1 to Answer 1"
    }
]

Answer 1

你可以使用json_arrayagg():

select a.*, json_arrayagg(c.content)
from Answer a inner join
     Comment c
     on c.answerId = a.answerId
where c.questionId = 1
group by a.answerId

Here 是一个 dbfiddle。

如果您想要所有行，即使是没有 cmets 的行，您可以使用：

select a.*, json_arrayagg(c.content)
from Answer a left join
     Comment c
     on c.answerId = a.answerId and
        c.questionId = 1
group by a.answerId

Answer 2

我只显示答案中的 answerid 和 questions1 其余的是GROUP BY AND GROUP_CONCAT

select a.answerId, a.questionId, GROUP_CONCAT(DISTINCT a.content) answerContent, GROUP_CONCAT(DISTINCT c.content) comments
from Answer a inner join Comment c on c.answerId = a.answerId 
where c.questionId = 1
GROUP BY a.answerId;

回答ID |问题ID |回答内容 |厘米 --------: | ---------: | :--------------- | :------------------------------------------------ --------- 1 | 1 |测试答案 1 |测试评论 1 到答案 1，测试评论 2 到答案 1 2 | 1 |测试答案 2 |测试评论 1 到答案 2，测试评论 2 到答案 2

select a.answerId, a.questionId, a.content answerContent, c.content comments
from Answer a inner join Comment c on c.answerId = a.answerId 
where c.questionId = 1
;

回答ID |问题ID |回答内容 |厘米 --------: | ---------: | :--------------- | :---------------------------- 1 | 1 |测试答案 1 |测试评论 1 到答案 1 1 | 1 |测试答案 1 |测试评论 2 到答案 1 2 | 1 |测试答案 2 |测试评论 1 到答案 2 2 | 1 |测试答案 2 |测试答案 2 的评论 2

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