如何更改 mysql 数据库查询？答案

【问题标题】：How can I change mysql db query?如何更改 mysql 数据库查询？
【发布时间】：2021-08-20 05:17:21
【问题描述】：

我想在 api 端点接收的数据是：

[
    {"Products":5,"Computer":2,"Handphone":3},
    {"Fruits":4,"Orange":2,"Apple":2},
    {"Consumables":6,"Tissue":2,"Wet Wipes":3, "Handkerchief":1}
]

所以产品类别包含电脑、手机。水果类包括橙子和苹果。消耗品类包括纸巾、湿纸巾和手帕

我在 mySQL 中有以下数据：

ID	Items	Category
1	Computer	Products
2	Handphone	Products
3	Computer	Products
4	Handphone	Products
5	Handphone	Products
6	Orange	Fruits
7	Orange	Fruits
8	Apple	Fruits
9	Apple	Fruits
10	Tissue	Consumables
11	Tissue	Consumables
12	Wet Wipes	Consumables
13	Wet Wipes	Consumables
14	Handkerchief	Consumables
15	Wet Wipes	Consumables

这是我用来在反应中进行数据库查询的代码：

app.get("/countintents", (req, res) => {
  db.query(
    "SELECT SUM(CASE WHEN intent IN ('Products', 'Land Transport') THEN 1 END) AS products, SUM(CASE WHEN intent IN ('Air Freight', 'Industry Solutions', 'Aerospace and Defense') THEN 1 END) AS industry_solutions, SUM(CASE WHEN intent in ('Profile', 'Contact Us') THEN 1 END) AS about_us FROM data_analytics",
    (err, result) => {
      if (err) {
        console.log(err);
      } else {
        res.send(result);
      }
    }
  );
});

我会问我的数据库查询应该是什么？

【问题讨论】：

标签： javascript mysql sql node.js reactjs

【解决方案1】：

您可以在数据库查询中获得组总数，如下所示。

SELECT category, items, count_items FROM(
        select items, category, count(items) count_items
        from <your_table>
        group by items, category
        UNION ALL
        SELECT Category, Category, Count(category)
        from <your_table>
        GROUP BY Category
    ) X ORDER BY category,count_items.

我正在检查您需要的结果是否支持 Mysql JSON。

【讨论】：

好的，我在我的问题中添加了列，如果我没有类别列，我还能使用 ALIAS 吗？

【解决方案2】：

您可以使用group by with rollup 构造值：

select category, item, count(*) as cnt
from t
group by category, item with rollup
having category is not null ;

您可以使用字符串聚合构造带有字符串的单独行：

select group_concat(coalesce(item, category), ':', cnt order by (item is null) desc, item)
from (select category, item, count(*) as cnt
      from t
      group by category, item with rollup
      having category is not null
     ) ci
group by category;

或作为 JSON 数组：

select json_arrayagg(json_object(coalesce(item, category), cnt))
from (select category, item, count(*) as cnt
      from t
      group by category, item with rollup
      having category is not null
     ) ci
group by category;

Here 是一个 dbfiddle。

【讨论】：