What are slowly changing dimensions?
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Answer Posted / chaitanya
SCD, is a technique used to store the historical value of
dimension attributes.
The values of dimensional attributes change as time goes by.
When these attribute values change, you can overwrite the
old values with the new ones, or you can
preserve the old value.
There are two methods of preserving the old attribute
values: you can store the old values as rows, or you can
store them as columns
three types of SCD:
• SCD type 1 overwrites the old values of the attributes so
the old values are not kept.
Ex: In product dimension,we will use SCD type 1, meaning we
will overwrite the old attribute values.
SCD type 2 keeps the old values by creating a new row for
each change.
SCD type 3 keeps the old values by putting them in another
column
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rank() over (partition by opt2.dim_plat_site_id, opt2.dim_site_opt_sid order by case when opt2.dm_market_flg in ('Y', 'U') then 1 else 2 end, lkp.contact_rank) as rank1, case opt2.contact_type when 'Buyer' then row_number() over (partition by opt2.dim_plat_site_id, opt2.dim_site_opt_sid, lkp.contact_rank order by has_name_flg desc, ship_to_flg desc , last_order_dt desc) when 'Decision Maker' then row_number() over (partition by opt2.dim_plat_site_id, opt2.dim_site_opt_sid, lkp.contact_rank order by has_name_flg desc , last_quote_dt desc , mailability_score desc , source_ranking desc) when 'Influencer' then row_number() over (partition by opt2.dim_plat_site_id, opt2.dim_site_opt_sid, lkp.contact_rank order by has_name_flg desc, mailability_score desc, source_ranking desc) when 'Payer' then row_number() over (partition by opt2.dim_plat_site_id, opt2.dim_site_opt_sid, lkp.contact_rank order by has_name_flg desc, mailability_score desc, source_ranking desc) --elu 05/28/2013 else row_number() over (partition by opt2.dim_plat_site_id, opt2.dim_site_opt_sid, lkp.contact_rank order by has_name_flg desc, mailability_score desc, source_ranking desc) end rank2 row_number() over (partition by opt3.dim_plat_site_id, opt3.dim_site_opt_sid order by rank1,rank2) as "rank", case when "rank"<= opt3.maximum_value then 'Y' else 'N' end as include_flg
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