Question

我正在寻找以下问题的sql语句：这是我表格的摘录

'from_city' 'to_city'
New York    Boston
Chicago     New York
New York    Los Angeles
Dallas      San Francisco
Miami       New York
Dallas      Los Angeles

预期结果应如下所示：

City              Count   Percentage
New York            4        33%
Los Angeles         2        17%
Dallas              2        17%
San Francisco       1         8%
Miami               1         8%
Chicago             1         8%
Boston              1         8%

所以我需要将两个列'from_city'和'to_city'联合起来，我可以用它：

(SELECT from_city AS City FROM table) UNION
(SELECT to_city AS City FROM table)

但现在我不知道如何应用结果集的计数和百分比。你能帮帮我吗？

提前致谢！

Answer 1

SELECT City, COUNT(*) AS Count, ROUND(100*COUNT(*)/total) AS Percentage
FROM (SELECT from_city AS City
      FROM table
      UNION ALL
      SELECT to_city AS City
      FROM table
     ) AS u
CROSS JOIN (SELECT 2 * COUNT(*) AS total
            FROM table) AS t
GROUP BY City
ORDER BY Count DESC

DEMO

Answer 2

SELECT
    cities.City,
    COUNT(*) as `Count`,
    CONCAT((COUNT(*) / (SELECT COUNT(*)*2 FROM table)) * 100, '%') as Percentage
FROM (
    SELECT from_city AS City FROM table UNION ALL
    SELECT to_city AS City FROM table
) as cities
GROUP BY cities.City

Answer 3

我相信以下查询将提供您想要的结果

SELECT 
  city, 
  count(*), 
  count(*)/(SELECT count(*)*2 FROM table)
FROM
  (SELECT from_city AS city FROM table
    union all
  SELECT to_city AS city FROM table) a
GROUP BY 
  city

Answer 4

您可能想要使用子查询：

SELECT
  city,
  COUNT(1) AS c,
  CONCAT(100*COUNT(1)/sums.total, '%') AS p
FROM
  (SELECT  from_city AS city FROM t
  UNION ALL
  SELECT to_city FROM t) AS cities
  CROSS JOIN
  (SELECT 
     COUNT(from_city)
    +COUNT(to_city) AS total
  FROM t) AS sums
GROUP BY
  city
ORDER BY 
  c DESC

- 注意，双重计数在常见情况下不起作用（因此使用两列的计数总和）检查demo。

此外，您还没有指定百分比格式 - 即应该包含多少个符号（因为它可能是非整数） - 所以我已将其保留原样

Mysql：联盟两列有计数

4 个答案: