Question

我有一张EMPLOYEES表：

employee_id(1) hire_date(15-2-2001)
employee_id(2) hire_date(2-2-1999)
employee_id(3) hire_date(11-2-2003)
employee_id(4) hire_date(6-7-2001)

我希望显示雇用的员工人数最多的年份，每月雇用的员工人数。我试过这个：

select extract (year from hire_date) 
from employees 
where max(count(employee_id))=count(employee_id) 
order by extract (year from hire_date);

我继续得到＆＃34; ORA-00934：这里不允许使用群组功能＆＃34;

我做错了什么？

我使用的是ORACLE 10g Express。

Answer 1

我们的想法是，您可以使用聚合和窗口函数来按月和年份获取总计。然后，您可以使用row_number()或dense_rank()选择最大的。

select ym.*
from (select ym.*, dense_rank() over (order by year_cnt, year) as seqnum
      from (select extract(year from hire_date) as yyyy,
                   extract(month from hire_date) as mm,
                   count(*) as cnt,
                   sum(count(*)) over (partition by extract(year from hire_date)) as year_cnt
            from employees 
            group by extract(year from hire_date),
                     extract(month from hire_date)
           ) ym
     ) ym
where seqnum = 1
order by yyyy, mm;

嗯，你可以在没有这么多子查询的情况下做到这一点：

with ym as (
      select extract(year from hire_date) as yyyy   
             extract(month from hire_date) as mm,
             count(*) as cnt,
             sum(count(*)) over (partition by extract(year from hire_date)) as yearcnt
      from employees 
      group by extract(year from hire_date), extract(month from hire_date)
     )
select *
from ym
where yearcnt = (select max(yearcnt) from ym)
order by yyyy, mm;

当然，如果两年具有相同的最大值，则会返回多年。

Answer 2

使用PL / SQL我发现了这个：

declare    
    recuperation float;
    CURSOR newRequest(recuperationDonnes float) is select count(employee_id) as nombreEmployes,
      extract(month from hire_date) as mois from employees where
      extract(year from hire_date) = (recuperationDonnes) group by extract(month from hire_date);
    a float;
    a1 float;
begin
    select extract (year from hire_date) as annee into recuperation from employees having count
     (employee_id)  >= all (select  count (employee_id) as emp from employees group by extract(year 
     from hire_date)) group by extract(year from hire_date);
     OPEN newRequest(recuperation);
     LOOP
        FETCH newRequest into a,a1;
        Exit when newRequest%NotFound;
        dbms_output.put_Line('Year: '||recuperation||' mois: '||a1||' nombreEmployes: '||a);
     END LOOP ;
     CLOSE newRequest;
end;

按查询分组的SQL顺序

2 个答案: