Versions Compared

Old Version 1

changes.mady.by.user Anand Vedam

Saved on

compared with

New Version 2

changes.mady.by.user Anand Vedam

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

In this article

Table of Contents
minLevel1
maxLevel2
absoluteUrltrue

This article emphasizes the different scenarios that are possible while performing an SCD2 operation and the behavior of the ELT SCD2 Snap, in each of these scenarios.

To follow these scenarios and configure the ELT SCD2 Snap properly in your SnapLogic environment, you will need to understand the following terms:

Term

Definition

Target Table Natural Key

A unique identifier based on which the SCD2 operation inserts a new record with different values for the same key in the target table.

Target Table Cause-Historization Field(s)

One or more fields in the target table which can cause new versions of data in the row.

For example, changes in Address or Employee Designation of an individual over a period of time. Each change in the address can cause a new version of the row (SCD Type2 entry) and so does each change in an employee’s designation.

Target Table Temporal Fields

A set of fields in the target table that store information specific to the validity of the cause-historization values in each of the row versions created. They can be a combination of the following fields:

  • Current row (Required): Boolean value to indicate if an entry is the current row.

  • Historical row (Required): Boolean value to indicate if an entry is a historical row.

  • Start date of current row (Required): Starting date-time for an entry to be the current row.

  • End date of current row (Optional) or End date of historical row (not chosen, by default): Date-time till when a current row entry remains current (becomes a historical row after that date-time passes by).

  • Invalid historical rows flag (Optional): An indicator for invalid rows in the target table. They are marked invalid due to lack of adequate historization information (logically incorrect values or null values) in the rows.

Info

For every natural key in the target table, there must be only one current row (valid now). All other entries (rows) for that natural key are either historical rows or invalid rows.

A change of value for a cause-historization field causes the existing current row to expire and the new entry (with the updated value) becomes the current row.

Scenario 1: Ideal SCD2 operation

Target table (Before)

Customer ID
(Natural Key)

Address
(Cause Historization Field)

Start Date
(Temporal Field 1)

End Date
(Temporal Field 2)

Current Row
(Temporal Field 3)

1

Chicago

1/1/18

12/1/18

false

1

New York

1/1/19

MAX_DATE

true

Source/Update table (Incoming SCD2 Data)

Customer ID (Natural Key)

Address (Cause Historization Values)

Start Date (Temporal Field 1)

1

Chicago

1/1/20

1

New York

1/1/21

Info

SCD2 Operation uses a row-by-row approach. The final current row is arrived at only after processing all rows for that natural key.

Output 1: Target table (After SCD2 operation)

Customer ID (Natural Key)

Address (New Cause Historization Entries)

Start Date
(Temporal Field 1)

End Date
(Temporal Field 2)

Current Row
(Temporal Field 3)

Remarks / Key Take-aways

1

Chicago

1/1/18

12/1/18

false

No change.

1

New York

1/1/19

1/1/20

false

Not current row anymore.

1

Chicago

1/1/20

1/1/21

false

New entry but not current row. Start date for the newer row is the End date for this entry.

1

New York

1/1/21

MAX_DATE

true

Current row with default End Date.