我将学生的评估存储在jsonb列调用评估中，数据库中的每一行都存储特定学科的学生评估，并且我试图获取一个查询来帮助检索： 1.对特定学科的学生评估。 2.学生对每门课程提供的所有学生评估。
这与我从表中选择所有记录时得到的结果相同。
[
{
"id": "22670f29-1437-4af1-b907-f6940377a851",
"sessionId": 3,
"sectionId": 4,
"subjectId": 8,
"assessment": [
{
"exam": 50,
"grdae": "A",
"total": 79,
"position": "First",
"student_id": 2,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Aristotle"
},
{
"exam": 50,
"grdae": "B",
"total": 69,
"position": "Third",
"student_id": 3,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Elvis"
}
]
},
{
"id": "beca9d97-0d0a-4d89-b8c5-c9a6fed812a5",
"sessionId": 3,
"sectionId": 4,
"subjectId": 10,
"assessment": [
{
"exam": 50,
"grdae": "A",
"total": 79,
"position": "First",
"student_id": 2,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Aristotle"
},
{
"exam": 50,
"grdae": "B",
"total": 69,
"position": "Third",
"student_id": 3,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Elvis"
}
]
},
{
"id": "1ed9c3d6-2482-4b1d-ab59-b77a8933699c",
"sessionId": 3,
"sectionId": 4,
"subjectId": 9,
"assessment": [
{
"exam": 50,
"grdae": "A",
"total": 90,
"position": "First",
"student_id": 2,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Aristotle"
},
{
"exam": 50,
"grdae": "B",
"total": 69,
"position": "Third",
"student_id": 3,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Elvis"
}
]
}
]
此结果包含对不同学科的评估，两个id为2和3的学生的subjectId为8、9和10。
注意：sessionID，SectionID和subjectId也是表调用评估中的列。
如果我想要一个id为2的学生，其subjectId为9，sessionId为3，sectionId为4，我应该可以得到这个对象：
{
"exam": 50,
"grdae": "A",
"total": 90,
"position": "First",
"student_id": 2,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Aristotle"
}
如果我想让一个学生对所有三个subjectId（即id 8、9、10和sessionId为3，sectionId为4：id 2）进行评估，则我应该是a：
[
{
"exam": 50,
"grdae": "A",
"total": 90,
"position": "First",
"student_id": 2,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Aristotle"
},
{
"exam": 50,
"grdae": "A",
"total": 79,
"position": "First",
"student_id": 2,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Aristotle"
},
{
"exam": 50,
"grdae": "A",
"total": 79,
"position": "First",
"student_id": 2,
"assessment_1": 9,
"assessment_2": 17,
"assessment_4": 5,
"student_name": "Anana Aristotle"
}
]
答案 0 :(得分：1)
将您的数据最小化到：
[
{
"sessionId": 3,
"sectionId": 4,
"subjectId": 8,
"assessment": [
{
"student_id": 2
},
{
"student_id": 3
}
]
},
{
"sessionId": 3,
"sectionId": 4,
"subjectId": 10,
"assessment": [
{
"student_id": 2
},
{
"student_id": 3
}
]
},
{
"sessionId": 3,
"sectionId": 4,
"subjectId": 9,
"assessment": [
{
"student_id": 2
},
{
"student_id": 3
}
]
}
]
第一步是取消相关ID信息的嵌套：
SELECT
assessments,
(elems ->> 'sessionId')::int as session_id,
(elems ->> 'sectionId')::int as section_id,
(elems ->> 'subjectId')::int as subject_id,
(assessments ->> 'student_id')::int AS student_id
FROM
mytable,
json_array_elements(jsondata) as elems,
json_array_elements(elems -> 'assessment') as assessments
结果是：
assessments | session_id | section_id | subject_id | student_id
:--------------- | ---------: | ---------: | ---------: | ---------:
{"student_id":2} | 3 | 4 | 8 | 2
{"student_id":3} | 3 | 4 | 8 | 3
{"student_id":2} | 3 | 4 | 10 | 2
{"student_id":3} | 3 | 4 | 10 | 3
{"student_id":2} | 3 | 4 | 9 | 2
{"student_id":3} | 3 | 4 | 9 | 3
json_array_elements()函数将json数组嵌套到每个数组元素一个记录中。因为有两个嵌套数组，所以您需要调用此函数两次。您可以在SELECT列表中看到每个级别的值。
之后，您可以在WHERE子句中过滤所需的任何内容。可以使用json_agg()聚合函数将结果记录（相关的评估对象）分组：
SELECT
json_agg(assessments)
FROM (
-- query from above
) s
WHERE session_id IN (3)
AND section_id IN (4)
AND subject_id IN (9) -- only one subject
AND student_id IN (2)
或
SELECT
json_agg(assessments)
FROM (
-- query from above
) s
WHERE session_id IN (3)
AND section_id IN (4)
AND subject_id IN (8,9,10) -- more subjects
AND student_id IN (2)