Question

这是我的用户数据库：

unordered_map<string, int> word_counts;

for (const auto& str : words) {
    word_counts[str]++;
}

auto cmp = [&word_counts](const string &word1, const string &word2){
    auto iter = word_counts.find(word1);
    int count1 = (iter != word_counts.end()) ? iter->second : 0;
    iter = word_counts.find(word2);
    int count2 = (iter != word_counts.end()) ? iter->second : 0;
    /* or, throw an exception if word1 or word2 are not found...
    int count1 = word_counts.at(word1);
    int count2 = word_counts.at(word2);
    */
    if (count1 == count2)
        return word1 < word2;
    return count1 > count2; // <-- why > and not < ?
};

我使用以下查询来返回：

（1）趋向女性

（2）其余女性

（3）男性趋向

（4）其余男性

id | sex    | trending | date_registered
---+--------+----------+----------------
1  | male   | 1        | 29-04-2020
2  | male   | 1        | 28-04-2020
3  | male   | 0        | 27-04-2020
4  | female | 1        | 26-04-2020
5  | female | 1        | 25-04-2020
6  | female | 0        | 24-04-2020
7  | female | 0        | 23-04-2020
8  | male   | 1        | 22-04-2020
9  | male   | 0        | 21-04-2020

here is the demo

最重要的是，我首先要针对每个case-when语句按最新用户进行排序。

例如select id, sex, trending, date_registered from users order by case when sex = 'female' and trending = 1 then 1 when sex = 'female' and trending = 0 then 2 when sex = 'male' and trending = 1 then 3 when sex = 'male' and trending = 0 then 4 end返回ASC排序，因此最早的用户将首先显示。

当我尝试对大小写进行DESC排序时（如波纹管），它什么都不会改变：

when sex = 'female' and trending = 1 then 1

Answer 1

根据您的要求，您需要按sex升序排列（因此，女性是第一位），trending降序排列（因此，趋势用户是第一位）和date_registered降序排列（因此最近的用户是第一位）

select
    id,
    sex,
    trending,
    date_registered
from users
order by sex, trending desc, date_registered desc

您的小提琴的输出：

id  sex     trending    date_registered
4   female  1           26-04-2020
5   female  1           25-04-2020
6   female  0           24-04-2020
7   female  0           23-04-2020
1   male    1           29-04-2020
2   male    1           28-04-2020
8   male    1           22-04-2020
3   male    0           27-04-2020
9   male    0           21-04-2020

Updated demo

Answer 2

我想您可以这样写：

order by sex, trending desc

Here是您的数据库小提琴。

Answer 3

仅在CASE块之后放置DESC（在END关键字之后）：

select
    id,
    sex,
    trending,
    date_registered
from users
order by
    case
        when sex = 'female' and trending = 1 then 1
        when sex = 'female' and trending = 0 then 2
        when sex = 'male' and trending = 1 then 3
        when sex = 'male' and trending = 0 then 4
    end DESC

对每个个案进行排序

3 个答案: