如何在日期范围内为每个月动态创建记录

Question

我在 table cp 中有以下日期：

start_date: 01/01/2017, end_date: 01/08/2017;
start_date: 01/04/2017, end_date: 01/07/2017

我想为这些时间段之间的每个月动态创建一条记录。它尝试了以下查询，但我不明白为什么它不起作用。

select add_months(cp.end_date, rownum-1) which_month, id
FROM    (select '1' as id, 
            to_date('01/01/2017', 'DD/MM/YYYY') start_date,
            to_date('01/08/2017', 'DD/MM/YYYY') end_date
    from dual
    UNION
    select  '2' as id, 
            to_date('01/04/2017', 'DD/MM/YYYY') start_date,
            to_date('01/07/2017', 'DD/MM/YYYY') end_date
    from dual) cp, all_objects
WHERE ROWNUM <= months_between(cp.end_date, add_months(cp.start_date, -1));

你能帮帮我吗？

Answer 1

I don't understand why it's not working.

ROWNUM是结果集生成的伪列；它并不像你想的那样工作。

一个解决方案 - 有多种解决方案，但这是最接近行业标准的 - 是使用 connect by level 技巧：

select '1' as id, 
        add_months(date '2017-01-01', (level-1) ) as which_month
from dual
connect by level <= months_between(date '2017-08-01', date '2017-01-01')+1

months_between() 采用参数 (end_date, start_date) - 您需要将该数字加一以获得结束日期。

"Would the level-trick still work ?"

有点。有一个额外的技巧可以防止 CONNECT BY 生成一个产品：

select id, 
        add_months(start_date, level-1 ) as which_month
from t23
connect by level <= months_between(end_date , start_date)+1
    --  these two lines required to avoid the need for DISTINCT
    and id = prior id 
    and prior sys_guid() is not null
order by 1, 2
;

LiveSQL demo.

Answer 2

使用 APC 的回答，非常感谢，我能够创建以下查询：

select distinct add_months(cp.start_date, level-1) which_month, id
FROM    (select '1' as id, 
        to_date('01/01/2017', 'DD/MM/YYYY') start_date,
        to_date('01/08/2017', 'DD/MM/YYYY') end_date
    from dual
    UNION
    select  '2' as id, 
        to_date('01/04/2017', 'DD/MM/YYYY') start_date,
        to_date('01/07/2017', 'DD/MM/YYYY') end_date
   from dual) cp
connect by level <= months_between(cp.end_date, cp.start_date) + 1
order by id asc, which_month asc;

我不得不在第一个 select 语句中使用不同的，但它为每个月（在各自的时间段内）的 table 'cp' 动态记录中的每个时间段创建。

更新

使用水平技巧，我能够构建解决方案：

select add_months(cp.start_date, level-1) which_month, id
FROM    (select '1' as id, 
        to_date('01/01/2017', 'DD/MM/YYYY') start_date,
        to_date('01/08/2017', 'DD/MM/YYYY') end_date
    from dual
    UNION
    select  '2' as id, 
        to_date('01/04/2017', 'DD/MM/YYYY') start_date,
        to_date('01/07/2017', 'DD/MM/YYYY') end_date
    from dual) cp
connect by level <= months_between(cp.end_date, cp.start_date) + 1
and id = prior id
and prior sys_guid() is not null
order by id asc, which_month asc;

如何在日期范围内为每个月动态创建记录

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