有没有办法在 SQL 中基于另一个 id 保持分组的同时基于一个 id 交替结果的顺序？答案

【问题标题】：Is there a way to alternate the order of a result based off one id while keeping groupings based off another id in SQL?有没有办法在 SQL 中基于另一个 id 保持分组的同时基于一个 id 交替结果的顺序？
【发布时间】：2020-12-30 12:12:14
【问题描述】：

我在 Postgresql 中有这个查询：

(SELECT q.question, q.category_id, a.id, a.question_id, a.answer
    FROM questions q, answers a
    WHERE q.id = a.question_id
    AND category_id = 1
    AND question_id
    BETWEEN (SELECT property FROM users WHERE email = 'test@test.com')
    AND (SELECT property FROM users WHERE email = 'test@test.com') + 14)
    
    UNION
    
(SELECT q.question, q.category_id, a.id, a.question_id, a.answer
    FROM questions q, answers a
    WHERE q.id = a.question_id
    AND category_id = 2
    AND question_id
    BETWEEN (SELECT laws FROM users WHERE email = 'test@test.com')
    AND (SELECT laws FROM users WHERE email = 'test@test.com') + 16)
    
ORDER BY question_id, id

当前以这种格式返回结果：

+-----------------------------+-------------+-------------+--------+
|          question           | category_id | question_id | answer |
+-----------------------------+-------------+-------------+--------+
| What color is the sky?      |           1 |          16 | blue   |
| What color is the sky?      |           1 |          16 | green  |
| What color is the sky?      |           1 |          16 | purple |
| What color is the sky?      |           1 |          16 | red    |
| What color is a firetruck?  |           1 |          17 | orange |
| What color is a firetruck?  |           1 |          17 | teal   |
| What color is a firetruck?  |           1 |          17 | red    |
| What color is a firetruck?  |           1 |          17 | green  |
| What color is dirt?         |           2 |          18 | green  |
| What color is dirt?         |           2 |          18 | green  |
| What color is dirt?         |           2 |          18 | green  |
| What color is dirt?         |           2 |          18 | green  |
+-----------------------------+-------------+-------------+--------+

我想要做的是根据 category_id 交替顺序，因此类别 id 将像这样交替：1、2、1、2，但我想根据 question_id 保留组。所以结果应该是这样的：

+-----------------------------+-------------+-------------+--------+
|          question           | category_id | question_id | answer |
+-----------------------------+-------------+-------------+--------+
| What color is the sky?      |           1 |          16 | blue   |
| What color is the sky?      |           1 |          16 | green  |
| What color is the sky?      |           1 |          16 | purple |
| What color is the sky?      |           1 |          16 | red    |
| What color is dirt?         |           2 |          18 | green  |
| What color is dirt?         |           2 |          18 | green  |
| What color is dirt?         |           2 |          18 | green  |
| What color is dirt?         |           2 |          18 | green  |
| What color is a firetruck?  |           1 |          17 | orange |
| What color is a firetruck?  |           1 |          17 | teal   |
| What color is a firetruck?  |           1 |          17 | red    |
| What color is a firetruck?  |           1 |          17 | green  |
+-----------------------------+-------------+-------------+--------+

我尝试过使用ORDER BY row_number() OVER (PARTITION BY t.category_id ORDER BY t.category_id) 但这只会导致每个都被交替而不被 question_id 分组

【问题讨论】：

标签： sql postgresql sql-order-by union window-functions

【解决方案1】：

我认为您想要以下order by 子句：

order by 
    rank() over(partition by category_id order by question_id),
    question_id,
    id

基本上这会交错类别/问题元组。

注意事项：

使用标准的显式连接 (from ... join ... on) 而不是老式的隐式连接 (from ..., ... where ...)；这是史前语法，不应在新代码中使用
很有可能您的查询可以简化为不使用union；如果您要使用示例数据和期望的结果提出另一个问题，那么您可能会提出建议

【讨论】：