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我正在阅读带有问题和预期输出的练习工作表。最后一个问题对我来说很难理解。任何人都可以帮忙吗？

问题

创建一个查询以显示员工总数以及 2005 年、2006 年、2007 年和 2008 年雇用的员工总数。

预期的输出格式

Total 2005 2006 2007 2008
107   29   24   19   11

以下是我尝试通过单独的查询获得结果

TO_CHAR(hire_date,'YYYY')
SELECT COUNT(employee_id) AS "Total"
FROM employees;

SELECT COUNT(employee_id) AS "2005"
FROM employees
WHERE TO_CHAR(hire_date,'YYYY') LIKE '2005' GROUP BY TO_CHAR(hire_date,'YYYY') ;

SELECT COUNT(employee_id) AS "2006"
FROM employees
WHERE TO_CHAR(hire_date,'YYYY') LIKE '2006' GROUP BY TO_CHAR(hire_date,'YYYY') ;

SELECT COUNT(employee_id) AS "2007"
FROM employees
WHERE TO_CHAR(hire_date,'YYYY') LIKE '2007' GROUP BY TO_CHAR(hire_date,'YYYY') ;

SELECT COUNT(employee_id) AS "2008"
FROM employees
WHERE TO_CHAR(hire_date,'YYYY') LIKE '2008' GROUP BY TO_CHAR(hire_date,'YYYY') ;

非常感谢任何将结果作为一个查询产生的帮助。

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2 回答 2

2

要将这些放在列中，请使用条件聚合：

select count(*) as Total,
       sum(case when to_char(hire_date, 'yyyy') = '2005' then 1 else 0 end) as "2005",
       sum(case when to_char(hire_date, 'yyyy') = '2006' then 1 else 0 end) as "2006",
       sum(case when to_char(hire_date, 'yyyy') = '2007' then 1 else 0 end) as "2007",
       sum(case when to_char(hire_date, 'yyyy') = '2008' then 1 else 0 end) as "2008"
from employees
where to_char(hire_date, 'yyyy') in ('2005', 2006', '2007', '2008')
于 2013-04-01T19:36:00.307 回答
1

您正在尝试对数据进行透视，因此您可以使用现有查询，但CASE在聚合内添加一个表达式：

SELECT COUNT(employee_id) AS "Total",
    sum(case when TO_CHAR(hire_date,'YYYY') = '2005' then 1 else 0 end) "2005",
    sum(case when TO_CHAR(hire_date,'YYYY') = '2006' then 1 else 0 end) "2006",
    sum(case when TO_CHAR(hire_date,'YYYY') = '2007' then 1 else 0 end) "2007",
    sum(case when TO_CHAR(hire_date,'YYYY') = '2008' then 1 else 0 end) "2008"
FROM employees;

根据您的 Oracle 版本，您可能可以使用该PIVOT功能：

select *
from
(
  select count(*) over() Total,
    TO_CHAR(hire_date,'YYYY') Year
  from employees
) 
pivot
(
    count(Year)
    for Year in ('2005', '2006', '2007', '2008')
)

查看两个查询的演示

于 2013-04-01T19:36:59.550 回答