将行更改为列并计数

Question

如何根据行计算计数？

消息表 每个员工可以休2天

Employee-----First_Day_Off-----Second_Day_Off
1------------10/21/2009--------12/6/2009
2------------09/3/2009--------12/6/2009
3------------09/3/2009--------NULL
4
5
.
.
.

现在我需要一张表格，显示当天起飞的日期和人数

Date---------First_Day_Off-------Second_Day_Off
10/21/2009---1-------------------0
12/06/2009---1--------------------1
09/3/2009----2--------------------0

有什么想法吗？

Answer 1

Oracle 9i +，使用子查询因子分析（WITH）：

WITH sample AS (
   SELECT a.employee,
          a.first_day_off AS day_off,
          1 AS day_number
     FROM YOUR_TABLE a
    WHERE a.first_day_off IS NOT NULL
   UNION ALL
   SELECT b.employee,
          b.second_day_off,
          2 AS day_number
     FROM YOUR_TABLE b
    WHERE b.second_day_off IS NOT NULL)
  SELECT s.day_off AS date,
         SUM(CASE WHEN s.day_number = 1 THEN 1 ELSE 0 END) AS first_day_off,
         SUM(CASE WHEN s.day_number = 2 THEN 1 ELSE 0 END) AS second_day_off
    FROM sample s
GROUP BY s.day_off

非子查询版本

  SELECT s.day_off AS date,
         SUM(CASE WHEN s.day_number = 1 THEN 1 ELSE 0 END) AS first_day_off,
         SUM(CASE WHEN s.day_number = 2 THEN 1 ELSE 0 END) AS second_day_off
    FROM (SELECT a.employee,
                 a.first_day_off AS day_off,
                 1 AS day_number
            FROM YOUR_TABLE a
           WHERE a.first_day_off IS NOT NULL
          UNION ALL
          SELECT b.employee,
                 b.second_day_off,
                 2 AS day_number
            FROM YOUR_TABLE b
           WHERE b.second_day_off IS NOT NULL) s
GROUP BY s.day_off

Answer 2

处理这些查询有点尴尬，因为你有几天存储在不同的列中。更好的布局是拥有像

这样的东西

EMPLOYEE_ID    DAY_OFF

如果员工休息多天，那么你会有多行

EMPLOYEE_ID    DAY_OFF
1              10/21/2009
1              12/6/2009
2              09/3/2009
2              12/6/2009
3              09/3/2009
...

在这种情况下，您可以使用以下查询了解每个人休息的天数：

SELECT EMPLOYEE_ID, COUNT(*) AS NUM_DAYS_OFF FROM DAYS_OFF_TABLE GROUP BY EMPLOYEE_ID

每个日期休假的人数如下：

SELECT DAY_OFF, COUNT(*) AS NUM_PEOPLE FROM DAYS_OFF_TABLE GROUP BY DAY_OFF

但我离题了......

您可以尝试使用SQL CASE语句来帮助解决此问题：

SELECT Employee, CASE
    WHEN First_Day_Off is NULL AND Second_Day_Off is NULL THEN 0
    WHEN First_Day_Off is NOT NULL AND Second_Day_Off is NULL THEN 1
    WHEN First_Day_Off is NULL AND Second_Day_Off is NOT NULL THEN 1
    ELSE 2
    END AS NUM_DAYS_OFF
FROM DAYS_OFF_TABLE

（请注意，根据您的数据库，您可能需要稍微改变一下语法。

获取当天起飞的日期和人数可能会更复杂。

我不知道这是否有用，但你可以尝试一下：

SELECT
    Date_Off,
    COUNT(*) AS Num_People
FROM
    (SELECT
        First_Day_Off, COUNT(*) AS Num_People FROM DAYS_OFF_TABLE WHERE First_Day_Off IS NOT NULL GROUP BY First_Day_Off
    UNION
    SELECT Second_Day_Off, COUNT(*) AS Num_People FROM DAYS_OFF_TABLE WHERE Second_Day_Off IS NOT NULL GROUP BY Second_Day_Off)
GROUP BY
    Num_People