Oracle：根据一列日期返回特定记录

Answer 1

今天是 9 月 22 日，所以 - 这行吗？

一些样本数据：

SQL> with test (period, month, start_date) as
  2    (select  1, 'april'    , date '2022-04-01' from dual union all
  3     select  5, 'august'   , date '2022-08-06' from dual union all
  4     select  6, 'september', date '2022-09-03' from dual union all
  5     select  7, 'october'  , date '2022-10-01' from dual union all
  6     select 10, 'january'  , date '2023-01-01' from dual union all
  7     select 12, 'march'    , date '2023-03-04' from dual
  8    ),

查询从这里开始：

  9  temp as
 10    (select period, month, start_date,
 11       row_number() over (order by start_date desc) rn
 12     from test
 13     where start_date <= sysdate
 14    )
 15  select period
 16  from temp
 17  where rn = 1
 18   /

    PERIOD
----------
         6

SQL>

它仍然使用子查询（或 CTE，如我的示例），但是 - 与您的方法相反，它仅从源表中选择一次，因此应该提高性能。

---

更多测试：而不是 sysdate（第 13 行），假设今天是 9 月 2 日（这意味着它在第 5 期）：

  9  temp as
 10    (select period, month, start_date,
 11       row_number() over (order by start_date desc) rn
 12     from test
 13     where start_date <= date '2022-09-02'
 14    )
 15  select period
 16  from temp
 17  where rn = 1;

    PERIOD
----------
         5

SQL>

或者，如果今天是 8 月 7 日：

  9  temp as
 10    (select period, month, start_date,
 11       row_number() over (order by start_date desc) rn
 12     from test
 13     where start_date <= date '2022-08-07'
 14    )
 15  select period
 16  from temp
 17  where rn = 1;

    PERIOD
----------
         5

SQL>

Answer 2

您对 start_date 的规则似乎是：

• 如果月份是一月（日历年的第一个月）或四月（通常是财政年度的第一个月），则使用该月的第一天；
• 否则使用每月的第一个星期六。

如果是这种情况，那么您可以计算下个月的开始日期并使用查询：

SELECT *
FROM   table1
WHERE  start_date <= SYSDATE
AND    SYSDATE < CASE
                 WHEN EXTRACT(MONTH FROM ADD_MONTHS(start_date, 1))
                      IN (1, 4) -- 1st month of calendar or financial year
                 THEN TRUNC(ADD_MONTHS(start_date, 1), 'MM')
                 ELSE NEXT_DAY(TRUNC(ADD_MONTHS(start_date, 1), 'MM') - 1, 'SATURDAY')
                 END

然后，对于您的示例数据：

CREATE TABLE table1 (
  period     NUMBER(2,0),
  month      VARCHAR2(9)
             GENERATED ALWAYS AS (
               CAST(
                 TO_CHAR(start_date, 'FXMonth', 'NLS_DATE_LANGUAGE=English')
                 AS VARCHAR2(9)
               )
             ),
  start_date DATE
);

INSERT INTO table1 (period, start_date)
  SELECT LEVEL,
         CASE
         WHEN EXTRACT(MONTH FROM ADD_MONTHS(DATE '2022-04-01', LEVEL - 1))
              IN (1, 4) -- 1st month of calendar or financial year
         THEN ADD_MONTHS(DATE '2022-04-01', LEVEL - 1)
         ELSE NEXT_DAY(ADD_MONTHS(DATE '2022-04-01', LEVEL - 1) - 1, 'SATURDAY')
         END
  FROM   DUAL
  CONNECT BY LEVEL <= 12;

输出：

PERIOD	MONTH	START_DATE
6	September	2022-09-03 00:00:00

fiddle