Problem 2 of 5 · Slowly-changing dimensionsNext: Detect which attribute changed per version

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Practice / SQL / Slowly-changing dimensions

WorkingGuided

EasyAbout 8 minSlowly-changing dimensions

Distinct email versions per customer

Count the distinct non-NULL emails each customer has ever had in dupes — a proxy for how volatile the attribute is. Ignore NULLs and exact duplicate rows. Sort by customer_id.

Returncustomer_iddistinct_emails

Columns

dupes4 columns

columntype

customer_idVARCHAR

emailVARCHAR

phoneVARCHAR

loaded_tsTIMESTAMP WITH TIME ZONE

The table

9 rows · 4 columns

dupesfirst 5 of 9 rows

customer_idemailphoneloaded_ts

c_001alice@old.com+1-111-11112026-05-01 10:00:00

c_001alice@new.comNULL2026-05-15 10:00:00

c_001NULL+1-111-22222026-05-20 10:00:00

c_002bob@example.com+1-222-22222026-06-01 09:00:00

c_003carol@example.com+1-333-33332026-04-01 08:00:00

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