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what is difference between scd2 and scd3
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Answer / rashmirekha panigrahy
In SCD Type2 we keep the entire historical data in the dimension table whereas in SCD Type3 we keep partial historical data in the dimension table.
For Ex : Suppose we are having a Customer Table. Acustomer 1st staying at Los Angels. Then he is shifted to DEllas. again he is shifted to Texas.
In case of Type 2 if we are using date method it will show the location and how many days he stayed on that particular location.
Sk_C Cust_ID Cust_NM Location Start_Dt End_DT
101 200345 Williams Los Angels 01-Mar-2011 23-Jun-2012
678 200345 Williams Dellas 24-Jun-2012 12-Nov-2014
1562 200345 Williams Texas 13-Nov-2014 NULL
But In case of Type 3 we will keep only current location and previous location. Not more than that.
Sk_C Cust_ID Cust_NM Cur_Location Pre_Location
101 200345 Williams Los Angels NULL
He shifted to Dellas.
Sk_C Cust_ID Cust_NM Cur_Location Pre_Location
101 200345 Williams Dellas Los Angels
Again he shifted to Texas.
Sk_C Cust_ID Cust_NM Cur_Location Pre_Location
101 200345 Williams Texas Dellas
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According to my findings, the key difference between SCD type 2 and type 3 is in their ability to maintain historical records. SCD type 2 is capable of storing multiple versions of a record, while SCD type 3 may only retain the current version and one previous version. However, there is some ambiguity regarding how many records SCD type 3 can hold.
To clarify, a good rule of thumb is to use SCD type 3 when the number of historic records that need to be retained is known in advance for e.g. If you need to store 5 records per user_id then the data structure is going to remain consistent over time i.e. 5 records hence implementing type 3 SCD will be a better choice. Conversely, if the number of records per user_id is uncertain, SCD type 2 may be a better choice.
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