Problem 5 of 11 · Data quality & validationNext: Find duplicate contacts once the key is normalised

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Practice / SQL / Data quality & validation

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MediumAbout 6 minData quality & validation

Find fully-identical duplicate rows

Find rows in dupes that are exact duplicates — identical on every column. Return customer_id, email, phone, and copies (how many identical rows). Sort by customer_id.

Columns

dupes4 columns

columntype

customer_idVARCHAR

emailVARCHAR

phoneVARCHAR

loaded_tsTIMESTAMP WITH TIME ZONE

The table

14 rows · 4 columns

dupesfirst 5 of 14 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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