SQL JOIN 查询中的重复条目
Repetitive entries in SQL JOIN query
我有三个table帖子、评论和用户 . posts table 包括两种类型的帖子，question 和 answer。对问题和答案进行评论。我的目的是获得一个带有评论、答案和答案评论的问题。我还需要用户 table 的用户名作为我获取的每个问题、答案和评论的作者。我正在使用 Postgres 9.5，并使用 json_agg() 函数。
虽然我需要的示例输出应该类似于以下第一个，但我得到了重复的条目。
我在这里缺少什么？正确的 group by 子句可能是。或者用他们的评论收集答案的子查询不是这样做的方法。当我从评论 table 的帖子中注释掉左连接时，我得到了想要的结果而没有对问题发表评论。此外，当我取消包含子查询的左连接时，我得到了预期的非重复结果，而且这也不是我想要的完整数据集。这些是我到目前为止为解决问题而收集的东西。
我需要的：
[
{
"post_id": "10",
"created_at": "2016-05-10T00:16:54.469Z",
"post_type": "question",
"post_title": "qwerty",
"post_text": "asdasd asda sdasd",
"post_author_id": 1,
"author": "isikfsc",
"parent_post_id": null,
"is_accepted": null,
"acceptor_id": null,
"answers": [
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"author": "isikfsc",
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 17
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"author": "isikfsc",
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 14
}
]
}
],
"comments": [
{
"id": 1,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 10
}
]
}
]
我的查询是：
SELECT
q.*,
json_agg(ac.*) AS answers,
json_agg(c.*) AS comments --comments on posts of post_id questions
FROM posts q
LEFT JOIN
(
SELECT
a.*,
json_agg(c.*) AS comments -- comments on posts of post_id answers
FROM posts a
LEFT JOIN comments c
ON a.post_id = c.parent_post_id
GROUP BY a.post_id
) ac
ON q.post_id = ac.parent_post_id
LEFT JOIN comments c
ON q.post_id = c.parent_post_id
WHERE q.post_id = 10
GROUP BY q.post_id
我得到的：
[
{
"post_id": "10",
"created_at": "2016-05-10T00:16:54.469Z",
"post_type": "question",
"post_title": "qwerty",
"post_text": "asdasd asda sdasd",
"post_author_id": 1,
"parent_post_id": null,
"is_accepted": null,
"acceptor_id": null,
"answers": [
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
}
],
"comments": [
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
}
]
}
]
所有参与方都加入后就会进行分组，因此聚合将取决于生成的基数。加入带有答案和评论的帖子会导致它们之间的完全连接，从而复制所有值。它们需要分开并单独执行，一种方法如下：
SELECT
q.*,
(SELECT json_agg(ac.*)
FROM (
SELECT a.*, json_agg(c.*) AS comments
FROM posts a
LEFT JOIN comments c ON (a.post_id = c.parent_post_id)
WHERE a.parent_post_id = q.post_id
GROUP BY a.post_id
) ac
) AS answers,
json_agg(c.*) AS comments --comments on posts of post_id questions
FROM posts q
LEFT JOIN comments c ON (q.post_id = c.parent_post_id)
WHERE q.post_id = 10
GROUP BY q.post_id;
或者：
SELECT q.*, qa.answers, qc.comments
FROM posts q
LEFT JOIN (
SELECT ac.parent_post_id, json_agg(ac.*) AS answers
FROM (
SELECT ac.*, json_agg(c.*) AS comments
FROM posts ac
LEFT JOIN comments c ON (c.parent_post_id = ac.post_id)
GROUP BY ac.post_id
) ac
GROUP BY ac.parent_post_id
) qa ON (qa.parent_post_id = q.post_id)
LEFT JOIN (
SELECT c.parent_post_id, json_agg(c.*) AS comments
FROM comments c
GROUP BY c.parent_post_id
) qc ON (qc.parent_post_id = q.post_id)
WHERE q.post_id = 10;
我有三个table帖子、评论和用户 . posts table 包括两种类型的帖子，question 和 answer。对问题和答案进行评论。我的目的是获得一个带有评论、答案和答案评论的问题。我还需要用户 table 的用户名作为我获取的每个问题、答案和评论的作者。我正在使用 Postgres 9.5，并使用 json_agg() 函数。
虽然我需要的示例输出应该类似于以下第一个，但我得到了重复的条目。
我在这里缺少什么？正确的 group by 子句可能是。或者用他们的评论收集答案的子查询不是这样做的方法。当我从评论 table 的帖子中注释掉左连接时，我得到了想要的结果而没有对问题发表评论。此外，当我取消包含子查询的左连接时，我得到了预期的非重复结果，而且这也不是我想要的完整数据集。这些是我到目前为止为解决问题而收集的东西。
我需要的：
[
{
"post_id": "10",
"created_at": "2016-05-10T00:16:54.469Z",
"post_type": "question",
"post_title": "qwerty",
"post_text": "asdasd asda sdasd",
"post_author_id": 1,
"author": "isikfsc",
"parent_post_id": null,
"is_accepted": null,
"acceptor_id": null,
"answers": [
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"author": "isikfsc",
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 17
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"author": "isikfsc",
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 14
}
]
}
],
"comments": [
{
"id": 1,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"author": "isikfsc",
"parent_post_id": 10
}
]
}
]
我的查询是：
SELECT
q.*,
json_agg(ac.*) AS answers,
json_agg(c.*) AS comments --comments on posts of post_id questions
FROM posts q
LEFT JOIN
(
SELECT
a.*,
json_agg(c.*) AS comments -- comments on posts of post_id answers
FROM posts a
LEFT JOIN comments c
ON a.post_id = c.parent_post_id
GROUP BY a.post_id
) ac
ON q.post_id = ac.parent_post_id
LEFT JOIN comments c
ON q.post_id = c.parent_post_id
WHERE q.post_id = 10
GROUP BY q.post_id
我得到的：
[
{
"post_id": "10",
"created_at": "2016-05-10T00:16:54.469Z",
"post_type": "question",
"post_title": "qwerty",
"post_text": "asdasd asda sdasd",
"post_author_id": 1,
"parent_post_id": null,
"is_accepted": null,
"acceptor_id": null,
"answers": [
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 17,
"created_at": "2016-05-10T04:58:56.350229",
"post_type": "answer",
"post_title": null,
"post_text": "222asda dasdad asdada",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 5,
"created_at": "2016-05-10T10:56:30.220128",
"text": "qweqwe",
"author_id": 1,
"parent_post_id": 17
},
{
"id": 8,
"created_at": "2016-05-10T11:00:00.182991",
"text": "sasasd",
"author_id": 1,
"parent_post_id": 17
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
},
{
"post_id": 14,
"created_at": "2016-05-10T04:19:19.005556",
"post_type": "answer",
"post_title": null,
"post_text": "asdasdasdasd",
"post_author_id": 1,
"parent_post_id": 10,
"is_accepted": null,
"acceptor_id": null,
"comments": [
{
"id": 2,
"created_at": "2016-05-10T05:25:34.671008",
"text": "qeqweqwe",
"author_id": 1,
"parent_post_id": 14
}
]
}
],
"comments": [
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 1,
"created_at": "2016-05-10T05:25:28.200327",
"text": "asadasdad",
"author_id": 1,
"parent_post_id": 10
},
{
"id": 4,
"created_at": "2016-05-10T10:25:23.381177",
"text": "werwer",
"author_id": 1,
"parent_post_id": 10
}
]
}
]
所有参与方都加入后就会进行分组，因此聚合将取决于生成的基数。加入带有答案和评论的帖子会导致它们之间的完全连接，从而复制所有值。它们需要分开并单独执行，一种方法如下：
SELECT
q.*,
(SELECT json_agg(ac.*)
FROM (
SELECT a.*, json_agg(c.*) AS comments
FROM posts a
LEFT JOIN comments c ON (a.post_id = c.parent_post_id)
WHERE a.parent_post_id = q.post_id
GROUP BY a.post_id
) ac
) AS answers,
json_agg(c.*) AS comments --comments on posts of post_id questions
FROM posts q
LEFT JOIN comments c ON (q.post_id = c.parent_post_id)
WHERE q.post_id = 10
GROUP BY q.post_id;
或者：
SELECT q.*, qa.answers, qc.comments
FROM posts q
LEFT JOIN (
SELECT ac.parent_post_id, json_agg(ac.*) AS answers
FROM (
SELECT ac.*, json_agg(c.*) AS comments
FROM posts ac
LEFT JOIN comments c ON (c.parent_post_id = ac.post_id)
GROUP BY ac.post_id
) ac
GROUP BY ac.parent_post_id
) qa ON (qa.parent_post_id = q.post_id)
LEFT JOIN (
SELECT c.parent_post_id, json_agg(c.*) AS comments
FROM comments c
GROUP BY c.parent_post_id
) qc ON (qc.parent_post_id = q.post_id)
WHERE q.post_id = 10;