使用 postgresql 设计缓慢变化的维度类型 2 脚本

Question

假设我有以下目标表：

CREATE TABLE DimCustomer (
CustomerKey serial PRIMARY KEY,
    CustomerNum int NOT NULL,
    CustomerName varchar(25) NOT NULL,
    Planet varchar(25) NOT NULL,
    RowIsCurrent char(1) NOT NULL DEFAULT 'Y',
    RowStartDate date NOT NULL DEFAULT CURRENT_TIMESTAMP,
    RowEndDate date NOT NULL DEFAULT '12/31/9999'
);

INSERT INTO DimCustomer
(CustomerNum, CustomerName, Planet,  RowStartDate) 
VALUES (101,'Anakin Skywalker', 'Tatooine',   CURRENT_TIMESTAMP - INTERVAL '101 days'),
       (102,'Yoda', 'Coruscant',  CURRENT_TIMESTAMP - INTERVAL '100 days'),
       (103,'Obi-Wan Kenobi', 'Coruscant',  CURRENT_TIMESTAMP - INTERVAL '100 days')

我有一个以下暂存表：

CREATE TABLE Staging_DimCustomer
(
    CustomerNum int NOT NULL,
    CustomerName varchar(25) NOT NULL,
    Planet varchar(25) NOT NULL,
    ChangeDate date NOT NULL DEFAULT CURRENT_TIMESTAMP,
    RankNo int NOT NULL DEFAULT 1
)
INSERT INTO Staging_DimCustomer(CustomerNum, CustomerName, Planet, ChangeDate)
VALUES
(103,'Ben Kenobi', 'Coruscant',   CURRENT_TIMESTAMP - INTERVAL '99 days')

在暂存表中，看起来'Obi-Wan Kenobi'( customernum 103) 将他的名字更改为 'Ben Kenobi'。我想创建一个实现 scd 类型 2 并产生以下结果的脚本（缓慢改变维度类型 2）：

以下是我的尝试：

INSERT INTO DimCustomer (
  CustomerNum, CustomerName, Planet, RowIsCurrent, RowStartDate, RowEndDate
  ) 
 select CustomerNum, CustomerName, Planet, 'Y', ChangeDate, '12/31/9999'
 from Staging_DimCustomer 

 ON CONFLICT (CustomerNum) and RowIsCurrent = 'Y'
  DO UPDATE SET
    CustomerName = EXCLUDED.CustomerName,
    Planet = EXCLUDED.Planet,
    RowIsCurrent = 'N',
    RowEndDate = EXCLUDED.ChangeDate

我不知道如何查找已更改的值，更新现有行以将其淘汰，然后插入带有标志的新行rowiscurrent = 'Y'。我正在尝试根据这篇sql server文章 http://www.made2mentor.com/2013/08/how-to-load-slowly-changing-dimensions-using-t-sql-merge/对我的解决方案进行建模。

Answer 1

假设更改全部在最新行上，那么您可以更新当前行，然后插入：

with u as (
      update dimCustomer c
          set RowIsCurrent = 'N',
              RowEndDate = sc.ChangeDate
      from Staging_DimCustomer sc
      where sc.CustomerNum = c.CustomerNum and
            c.RowIsCurrent = 'Y'
     )
insert into dimCustomer (CustomerNum, CustomerName, Planet, RowIsCurrent, RowStartDate, RowEndDate
                         ) 
     select CustomerNum, CustomerName, Planet, 'Y', ChangeDate, '9999-12-31'::date
     from Staging_DimCustomer sc;

这假设更改发生在最新的记录上。实施历史性的改变是相当棘手的，我猜这是没有必要的。

请注意，您可能需要额外检查所插入的行实际上与当前行不同。

编辑：

如果您想避免对已存在的行进行更改，您可以执行以下操作：

with sc as (
      select *
      from Staging_DimCustomer
      where not exists (select 1
                        from DimCustomer c
                        where c.CustomerNum = sc.CustomerNum and
                              c.CustomerName = sc.CustomerName and
                              . . .  -- whatever other columns you want to check
                      )
     ),
     u as (
      update dimCustomer c
          set RowIsCurrent = 'N',
              RowEndDate = sc.ChangeDate
      from sc
      where sc.CustomerNum = c.CustomerNum and
            c.RowIsCurrent = 'Y'
     )
insert into dimCustomer (CustomerNum, CustomerName, Planet, RowIsCurrent, RowStartDate, RowEndDate
                         ) 
     select CustomerNum, CustomerName, Planet, 'Y', ChangeDate, '9999-12-31'::date
     from sc;