拉链表的展开算法_如何求展开式的系数

--建表语句  
--生成EDW_T00_H表(历史拉链表)  
-- Create table  
create table EDW_T00_H  
(  
  ID         VARCHAR2(2) not null,  
  START_DATE DATE not null,  
  STATUS     VARCHAR2(2),  
  END_DATE   DATE  
);  

-- Add comments to the table   
comment on table EDW_T00_H  
  is '历史拉链表';  
-- Add comments to the columns   
comment on column EDW_T00_H.ID  
  is 'ID';  
comment on column EDW_T00_H.START_DATE  
  is '开始日期';  
comment on column EDW_T00_H.STATUS  
  is '状态';  
comment on column EDW_T00_H.END_DATE  
  is '结束日期';  

-- Create/Recreate primary, unique and foreign key constraints   
alter table EDW_T00_H  
  add constraint EDW_T00_ID primary key (ID, START_DATE);  
--生成EDW_T00_ALL表(历史拉链展开后的表)  
-- Create table  
create table EDW_T00_ALL  
(  
  ID        VARCHAR2(2) not null,  
  DATA_DATE DATE not null,  
  STATUS    VARCHAR2(2) not null  
);  

-- Add comments to the table   
comment on table EDW_T00_ALL  
  is '历史拉链展开后的表';  
-- Add comments to the columns   
comment on column EDW_T00_ALL.ID  
  is 'ID';  
comment on column EDW_T00_ALL.DATA_DATE  
  is '数据日期';  
comment on column EDW_T00_ALL.STATUS  
  is '状态';  

--插入历史表测试数据  
insert into edw_t00_H (ID, START_DATE, STATUS, END_DATE)  
values ('3', to_date('01-12-2007', 'dd-mm-yyyy'), 'N', to_date('01-12-2009', 'dd-mm-yyyy'));  
insert into edw_t00_H (ID, START_DATE, STATUS, END_DATE)  
values ('3', to_date('01-12-2009', 'dd-mm-yyyy'), 'Y', to_date('16-12-2010', 'dd-mm-yyyy'));  
insert into edw_t00_H (ID, START_DATE, STATUS, END_DATE)  
values ('1', to_date('01-12-2010', 'dd-mm-yyyy'), 'Y', to_date('16-12-2010', 'dd-mm-yyyy'));  
insert into edw_t00_H (ID, START_DATE, STATUS, END_DATE)  
values ('2', to_date('01-12-2010', 'dd-mm-yyyy'), 'N', to_date('12-12-2010', 'dd-mm-yyyy'));  
COMMIT;  

主要用来取ROWNUM供第3步操作

--插入系统维护时间  
CREATE TABLE SYS_MATIAN_DATE(DATE_COL DATE);  
  
DECLARE  
  V_DATE     DATE := TO_DATE('20080101', 'YYYYMMDD');  
  V_DATE_MAX DATE;  
BEGIN  
  EXECUTE IMMEDIATE 'TRUNCATE TABLE SYS_MATIAN_DATE';  
  SELECT SYSDATE INTO V_DATE_MAX FROM DUAL;  
  WHILE V_DATE <= V_DATE_MAX LOOP  
    INSERT INTO SYS_MATIAN_DATE  
      SELECT V_DATE FROM DUAL;  
    V_DATE := V_DATE + 1;  
    COMMIT;  
  END LOOP;  
END;  
  
SELECT * FROM SYS_MATIAN_DATE;  

DECLARE  
  CURSOR LSLL_ID IS  
    SELECT ID,  
           START_DATE,  
           STATUS,  
           DECODE(END_DATE,  
                  TO_DATE('30001231', 'YYYYMMDD'),  
                  SYSDATE,      --TO_DATE(P_ETLDATE, 'YYYYMMDD'),  
                  END_DATE) END_DATE  
      FROM EDW_T00_H;  
  V_ID         VARCHAR2(1000);  
  V_START_DATE DATE;  
  V_END_DATE   DATE;  
  V_DATA_DATE  DATE;  
  V_STATUS     VARCHAR2(2);  
BEGIN  
  BEGIN  
    EXECUTE IMMEDIATE 'TRUNCATE TABLE EDW_T00_ALL';  
    OPEN LSLL_ID;  
    LOOP  
      FETCH LSLL_ID  
        INTO V_ID, V_START_DATE, V_STATUS, V_END_DATE;  
      EXIT WHEN LSLL_ID%NOTFOUND;  
      INSERT INTO EDW_T00_ALL  
        (ID, DATA_DATE, STATUS)  
        SELECT V_ID, V_START_DATE + ROWNUM - 1 AS DATA_DATE, V_STATUS  
          FROM SYS_MATIAN_DATE  
         WHERE V_START_DATE + ROWNUM - 1 < V_END_DATE;  
      COMMIT;  
    END LOOP;  
    CLOSE LSLL_ID;  
  END;  
END;  

第3步中，游标的START_DATE、END_DATE要根据实际情况，灵活变通；代码的EXECUTE IMMEDIATE 'TRUNCATE TABLE EDW_T00_ALL';需要不需要，根据实际情况来定；第2步中生成数据日期维护表，主要用来第3步

SELECT V_ID, V_START_DATE + ROWNUM - 1 AS DATA_DATE, V_STATUS

          FROM SYS_MATIAN_DATE

         WHERE V_START_DATE + ROWNUM - 1 < V_END_DATE;

取数用，目的是保证SYS_MATIAN_DATE表有足够的记录，以使对于每一条历史拉链表中的记录都能取得到；本文给出了我们进行拉链表展开时的一个思路。