In this article
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This article emphasizes lays emphasis on the different scenarios that are possible while performing an SCD2 operation and the behavior of the ELT SCD2 Snap, in each of these scenarios.
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Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | 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. |
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The SCD2 operation uses a row-by-row approach. The final current row is arrived at, only after processing all rows for that natural key. |
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Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | Remarks / Key Take-aways |
1 | Chicago | 1/1/18 | 12/1/18 | false | No change. |
1 | New York | 1/1/19 | 1/1/21 | false | Not current row anymore. Any end date for New York before 1/1/21 (start date for Boston) results in New York becoming a historical row. |
1 | Boston | 1/1/21 | MAX_DATE | true | Current row with default End Date. |
Scenario 3: Target Table is Empty and Source Table Contains Duplicate Values for Cause-Historization field
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Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | Remarks / Key Take-aways |
1 | Chicago | 1/1/15 (or 1/1/14) | 1/1/16 | false | End date arrived based on the start date of the next entry (in ascending order). |
1 | Boston | 1/1/16 | 1/1/18 | false | End date arrived based on the start date of the next entry (in ascending order). |
1 | Chicago | 1/1/18 | 1/1/20 | false | Any start date for Chicago outside the range 1/1/18 - 1/1/20 will be ignored. |
1 | Boston | 1/1/20 | MAX_DATE | true | Current row with default End Date. |
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The SCD2 operation sorts the source data records in the ascending order of their Start Dates when there is no row numbering (sequence) specified in the source data. |
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Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | Remarks / Key Take-aways |
1 | Chicago | 1/1/18 | 12/1/18 | false | No change. |
1 | New York | 1/1/19 | 1/1/21 | false | Not current row anymore. Any end date for New York before 1/1/21 (start date for Boston) results in New York becoming a historical row. |
1 | Boston | 1/1/21 | MAX_DATE | true | Current row with default End Date. |
Output 4.2: Target Table (After SCD2 operation) when Invalid rows are Logged
Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | Invalid | Remarks / Key Take-aways |
1 | Chicago | 1/1/18 | 12/1/18 | false | No change. | |
1 | New York | 1/1/19 | 1/1/21 | false | Not current row anymore. Any end date for New York before 1/1/21 (start date for Boston) results in New York becoming a historical row. | |
1 | Orlando | 1/1/17 | MIN_DATE | false | true | Invalid row logged with End Date defaulted to MIN_DATE. |
1 | Boston | 1/1/21 | MAX_DATE | true | Current row with default End Date. |
Scenario 5: One or more Start Dates in Source Rows contain NULLs
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Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | Remarks / Key Take-aways |
1 | Chicago | 1/1/18 | 12/1/18 | false | No change. |
1 | New York | 1/1/19 | 1/1/21 | false | Not current row anymore. Any end date for New York before 1/1/21 (start date for Boston) results in New York becoming a historical row. |
1 | Boston | 1/1/21 | MAX_DATE | true | Current row with default End Date. |
Output 5.2: Target Table (After SCD2 operation) when Invalid rows are Logged and Nulls Honored
Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | Invalid | Remarks / Key Take-aways |
1 | Chicago | 1/1/18 | 12/1/18 | false | No change. | |
1 | New York | 1/1/19 | 1/1/21 | false | Not current row anymore. Any end date for New York before 1/1/21 (start date for Boston) results in New York becoming a historical row. | |
1 | Orlando | NULL | MIN_DATE | false | true | NULL remains as is. Invalid row logged with End Date defaulted to MIN_DATE. |
1 | Boston | 1/1/21 | MAX_DATE | true | Current row with default End Date. |
Output 5.3: Target Table (After SCD2 operation) when the Pipeline is set to Return the Error upon Detecting Invalid rows
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Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | 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. Any end date for New York before 1/1/20 (start date for the next row) results in New York becoming a historical row. |
1 | NULL | 1/1/20 | 1/1/21 | false | A NULL entry made in the ascending order of the start dates. End Date added This row cannot be the current row. |
1 | Boston | 1/1/21 | MAX_DATE | true | Current row with default End Date. |
NULL | Miami | 1/1/22 | MAX_DATE | true | This entry, though included in the target table, does not correspond to the same Natural Key as the other entries, in this example. |
Output 6.2: Target Table (After SCD2 operation) when NULLs in Source and Target Tables are Ignored
Customer ID (Natural Key) | Address (New Cause Historization Entries) | Start Date | End Date | Current Row | Invalid | Remarks / Key Take-aways |
1 | Chicago | 1/1/18 | 12/1/18 | false | No change. | |
1 | New York | 1/1/19 | 1/1/21 | false | Not current row anymore. Any end date for New York before 1/1/21 (start date for Boston) results in New York becoming a historical row. Any entry (Start Date 1/1/20, in this case) containing a NULL is ignored. | |
1 | Boston | 1/1/21 | MAX_DATE | true | Current row with default End Date. |