NSMutableArray更改为副本，从而导致父NSMutableArray中的更改(NSMutableArray changes to the copy causing changes in the parent NSMutableArray as well)

 分区外连接可以帮助填写日历数据。 它类似于交叉连接，但对于非平凡的表大小可能表现更好。 
 
 交叉连接将连接集合A中的每一行与集合B中的每一行。 
 
 分区外连接将连接集合A中的每一行与集合B中的每个已定义子集。 
 
 以下示例仅根据您提供的计划数据生成日期范围。 因此，第14和第15不会出现，但这很容易修复。 
 
with schedules as
(
    --Schedule data.
    select 'bottle washer' position, 'Fred'   name, date '2013-01-02' startdate, date '2013-01-05' enddate from dual union all
    select 'bottle washer' position, 'Barney' name, date '2013-01-04' startdate, date '2013-01-07' enddate from dual union all
    select 'bottle washer' position, 'Betty'  name, date '2013-01-10' startdate, null              enddate from dual union all
    select 'bottle washer' position, 'Wilma'  name, date '2013-01-12' startdate, date '2013-01-13' enddate from dual union all
    select 'cook'          position, 'Bilbo'  name, date '2013-01-01' startdate, date '2013-01-03' enddate from dual union all
    select 'cook'          position, 'Frodo'  name, date '2013-01-05' startdate, date '2013-01-08' enddate from dual union all
    select 'cook'          position, 'Bilbo'  name, date '2013-01-07' startdate, null              enddate from dual
),
dates as
(
    --Date range, based on schedule data.
    select first_startdate + level - 1 the_date
    from
    (
        select min(startdate) first_startdate
            ,(max(enddate) - min(startdate))+1 date_diff
        from schedules
    )
    connect by level <= date_diff
)
--Count of staff working per position, per day.
select position, the_date, count(schedules.startdate) staffing
from dates
left join schedules partition by (position)
    on dates.the_date between schedules.startdate
        and nvl(schedules.enddate, date '9999-12-31')
group by position, the_date
order by position, the_date;

A partition outer join can help fill in calendar data. It is similar to a cross join but may perform much better with non-trivial table sizes.
 
A cross join will join every row in set A with every row in set B.
 
A partition outer join will join every row in set A with every defined subset in set B.
 
The example below generates the date range only based on the schedule data you provided. Therefore the 14th and 15th do not show up, but that can be easy to fix.
 
with schedules as
(
    --Schedule data.
    select 'bottle washer' position, 'Fred'   name, date '2013-01-02' startdate, date '2013-01-05' enddate from dual union all
    select 'bottle washer' position, 'Barney' name, date '2013-01-04' startdate, date '2013-01-07' enddate from dual union all
    select 'bottle washer' position, 'Betty'  name, date '2013-01-10' startdate, null              enddate from dual union all
    select 'bottle washer' position, 'Wilma'  name, date '2013-01-12' startdate, date '2013-01-13' enddate from dual union all
    select 'cook'          position, 'Bilbo'  name, date '2013-01-01' startdate, date '2013-01-03' enddate from dual union all
    select 'cook'          position, 'Frodo'  name, date '2013-01-05' startdate, date '2013-01-08' enddate from dual union all
    select 'cook'          position, 'Bilbo'  name, date '2013-01-07' startdate, null              enddate from dual
),
dates as
(
    --Date range, based on schedule data.
    select first_startdate + level - 1 the_date
    from
    (
        select min(startdate) first_startdate
            ,(max(enddate) - min(startdate))+1 date_diff
        from schedules
    )
    connect by level <= date_diff
)
--Count of staff working per position, per day.
select position, the_date, count(schedules.startdate) staffing
from dates
left join schedules partition by (position)
    on dates.the_date between schedules.startdate
        and nvl(schedules.enddate, date '9999-12-31')
group by position, the_date
order by position, the_date;