Question

Hi am trying to import data into my data warehouse and to simplify importing some data I want to make a new column in a table that will keep track of the most current value as I get new data.

My tables look like the following:

CREATE TABLE CustomerFact(
 Id INT IDENTITY PRIMARY KEY
,CustomerId NVARCHAR(20) NOT NULL --Current Id of a Customer
);

--Track changes to CustomerId
CREATE TABLE CustomerHistoryFact(
 Id INT IDENTITY PRIMARY KEY
,CurrentCustomerId NVARCHAR(20) --Most recent Customer Id
,CustomerId NVARCHAR(20) NOT NULL --Customer Id at time of record insert
,PrvsCustomerId NVARCHAR(20) NOT NULL --Customer Id at time of transaction
,PrvsCustomerIdEffectiveDate DATE NOT NULL --Date when PrvsCustomerId was effective
,PrvsCustomerIdObsoleteDate DATE NOT NULL --When the PrvsCustomerId was expired and replaced with a new Customer Id
);

The CustomerId, PrvsCustomerId, PrvsCustomerIdEffectiveDate, and PrvsCustomerIdObsoleteDate are all external. I want to assign a CurrentCustomerId whenever a new record is inserted.

This is determined by when a new CustomerHistoryFact is inserted, check the PrvsCustomerId with the CurrentCustomerId of all other records. If there is a match then the CustomerId of the new record becomes the CurrentCustomerId of all previous records or else the record is inserted and the CustomerId becomes the CurrentCustomerId.

Answer 1

Seems like a twisted database design. Why can’t you just keep on inserting CustomerId in CustomerHistoryFact table, everytime the CustomerFact record is updated? You can write a trigger on CustomerFact table for insert/update, and make an entry into CustomerHistoryFact table, if the latest CustomerId sorted by CustomerIdEffectiveDate desc is different from the customerId in Inserted/Deleted table. That way, you have a history of CustomerId’s for starting from current CustomerId to back to in time.

CREATE TABLE CustomerFact(
 Id INT IDENTITY PRIMARY KEY
,CustomerId NVARCHAR(20) NOT NULL --Current Id of a Customer
);

--Track changes to CustomerId
CREATE TABLE CustomerHistoryFact(
 Id INT IDENTITY PRIMARY KEY
,CustomerId NVARCHAR(20) --Most recent Customer Id
,PrevCustomerId NVARCHAR(20) NOT NULL --Customer Id at time of record insert
,UpdatedDate DATETIME NOT NULL --Date when PrvsCustomerId was effective
);

CREATE TRIGGER dbo.CustomerFact_IU
ON dbo.CustomerFact
AFTER INSERT, UPDATE
AS 
BEGIN
    SET NOCOUNT ON;

    --
    -- Check if this is an INSERT, UPDATE.
    -- 
    DECLARE @action as char(1);
    DECLARE @oldCustomerId NVARCHAR(20);

    SET @action = 'I'; -- Set Action to Insert by default.
    IF EXISTS(SELECT * FROM DELETED)
    SELECT @oldCustomerId = customerId from DELETED
    BEGIN
        SET @action = 
            CASE
                WHEN EXISTS(SELECT * FROM INSERTED) THEN 'U' -- Set Action to Updated.
                ELSE 'D' -- Set Action to Deleted.       
            END
    END
    ELSE 
        IF NOT EXISTS(SELECT * FROM INSERTED) RETURN; -- Nothing updated or inserted.

    IF @action = 'I' OR @action = 'U'
    BEGIN
         INSERT INTO dbo.CustomerHistoryFact
         SELECT CustomerId, @oldCustomerId, GETUTCDATE() FROM INSERTED 
    END 

    END