如何在 SQL 中进行列式和行式操作

Question

我对 SQL 查询中的行式和列式操作有疑问。我将使用以下示例数据 table:

来证明我的问题

Person           Income      Hours worked   Day
A                100         10             1
A                200         9              2
B                300         8              1 
B                400         7              2
C                500         6              1
C                600         5              2

我想编写一个查询，从中获取 (A + B) 和 C 的总收入、工作时间和每小时收入。即：

Person           Income      Hours worked   Income / Hour
A + B            1000        34             1000 / 34
C                1100        11             1100 / 11

我如何在 SQL 中执行此操作？

非常感谢！

Answer 1

您可以使用 case 表达式将包含 A、B 的行视为相同的行并汇总。

select 
case when person in ('A','B') then 'A+B' else person end as person
,sum(income) as income
,sum(hoursworked) as hoursworked
,sum(income)/sum(hoursworked) as income_hour
from yourtable
group by case when person in ('A','B') then 'A+B' else person end

Answer 2

您可以在子查询中使用 UNION ALL

SELECT Person, Income, [Hours worked], [Income / Hour]    
FROM (
  SELECT 'A + B' AS Person,
          SUM(Income) AS Income,
          SUM([Hours worked]) AS [Hours worked],
          SUM([Day]) AS [Hours worked]
  FROM dbo.TableName
  WHERE Person IN('A', 'B')           

  UNION ALL

  SELECT 'C' AS Person,
          SUM(Income) AS Income,
          SUM([Hours worked]) AS [Hours worked],
          SUM([Day]) AS [Hours worked]
  FROM dbo.TableName
  WHERE Person = 'C'
) x

如果要排序，可以在外部查询上应用 ORDER BY。

Answer 3

对于MySQL，我们可以这样做：

SELECT CASE WHEN t.Person IN ('A','B') THEN 'A + B' ELSE t.Person END AS Person
     , SUM(t.Income)                                                  AS Income
     , SUM(t.`Hours Worked`)                                          AS `Hours Worked`
     , CONCAT( SUM(t.Income) , ' / ' , SUM(t.`Hours Worked`) )        AS `Income / Hour`
 FROM mytable t
GROUP BY CASE WHEN t.Person IN ('A','B') THEN 'A + B' ELSE t.Person END

同样的模式适用于大多数其他关系数据库，但对转义不稳定的列名的处理不同。

对于 Oracle，用双引号而不是反引号将标识符括起来。（即用双引号替换反引号，并括起包含小写字母或其他特殊字符的列名。）

对于 SQL 服务器，将标识符括在方括号中... [Hours Worked].

Answer 4

只是为了提供另一种方法，这里有一个 UNION 方法：

SELECT 'A + B', sum(income) as income, sum(hoursworked) as hoursworked sum(income)/sum(hoursworked) as income_hour
FROM yourtable
WHERE person in ('A','B')

UNION ALL

SELECT person, sum(income) as income, sum(hoursworked) as hoursworked sum(income)/sum(hoursworked) as income_hour
FROM yourtable
WHERE person NOT in ('A','B')
GROUP BY person

编辑：蒂姆更快。

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