我如何联接两个以上的postgres表，并在postgres中将其作为nestedjson获得结果
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select categories.*, array_agg(questions.r_question) as theQuestions from categories
inner join
(select questions.*, json_build_object('question', questions.question) as r_question,
array_agg(answers.ans) as answeeer from questions)
questions on categories.category_id = questions.category_id
inner join
(select answers.*, json_build_object('answer', answers.answer) as ans from answers)
answers on questions.question_id = answers.question_id
group by categories.category_id;
我希望具有嵌入问题和嵌入答案的类别的数组
表结构
<pre>
quizx=# select * from categories
quizx-# ;
category_id | title | description
-------------+-------------------+--------------------------------
1 | Computer scicence | Quiz based on computer science
2 | General culture | Quiz based on general reality
3 | Chemistry | Quiz based on chemistry and so
8 | Capstone | Quiz based on chemistry and so
(4 rows)
quizx=# select * from answers;
answer_id | answer | correct | question_id
-----------+--------------------------+---------+-------------
1 | Instructions | 0 | 1
7 | Line length and wrapping | 0 | 2
8 | Control Structure | 1 | 2
4 | All of the above | 1 | 1
6 | Functions | 0 | 2
5 | Comments | 0 | 2
3 | Documents | 0 | 1
2 | Data Structures | 0 | 1
14 | cool stuff | 0 | 2
(9 rows)
quizx=# select * from questions;
question_id | question | category_id
-------------+----------------------------------------------------------------------------------------------------------------+-------------
1 | Software is defined as ____ | 1
2 | The rules of writing 'if-then-else', 'case-switch', 'while-until' and 'for' control flow statements are called | 1
4 | Who is it?? | 1
5 | slam | 2
6 | Is it good??? | 2
7 | test | 2
8 | again | 2
(7 rows)
</pre>我的查询的预期结果：
<pre>
[
"categoryId": 1,
"theCategory": "computer science ",
"description": "stuff about code\r\n",
"questions": [
"questionId": 9,
"theQuestion": "what year was the video game crash?",
"answers": [
"answerId": 22,
"theAnswer": "1985",
"correctAnswer": false
,
"answerId": 23,
"theAnswer": "1994",
"correctAnswer": false
,
"answerId": 24,
"theAnswer": "1983",
"correctAnswer": true
,
"answerId": 25,
"theAnswer": "1977",
"correctAnswer": false
]
,
"questionId": 11,
"theQuestion": "what language was the first commercially available?",
"answers": [
"answerId": 30,
"theAnswer": "java script",
"correctAnswer": false
,
"answerId": 31,
"theAnswer": "C",
"correctAnswer": false
,
"answerId": 32,
"theAnswer": "FORTRAN",
"correctAnswer": true
,
"answerId": 33,
"theAnswer": "ada",
"correctAnswer": false
]
,
"questionId": 12,
"theQuestion": "what is COBAL?",
"answers": [
"answerId": 34,
"theAnswer": "a business language used in many machines ",
"correctAnswer": true
,
"answerId": 35,
"theAnswer": "the first mainframe ",
"correctAnswer": false
,
"answerId": 36,
"theAnswer": "the first computer introduced ",
"correctAnswer": false
,
"answerId": 37,
"theAnswer": "the computer that introduced arpnet to the us military ",
"correctAnswer": false
]
]
,
"categoryId": 4,
"theCategory": "video games ",
"description": "this is about video games \r\n",
"questions": [
"questionId": 10,
"theQuestion": "what game was the iconic character Mario's first appearance?",
"answers": [
"answerId": 26,
"theAnswer": "donkey kong ",
"correctAnswer": true
,
"answerId": 27,
"theAnswer": "super mario bros ",
"correctAnswer": false
,
"answerId": 28,
"theAnswer": "mario bros",
"correctAnswer": false
,
"answerId": 29,
"theAnswer": "donkey kong country",
"correctAnswer": false
]
]
]
<pre>我收到以下错误：错误：表格“答案”缺少FROM子句条目LINE 7：array_agg（answers.ans）解答了问题...^SQL状态：42P01角色：212
答案
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