Problem 1 of 11 · Data quality & validationNext: How much duplication is in the feed?

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Practice / SQL / Data quality & validation

WorkingGuided

EasyAbout 4 minData quality & validation

Count duplicate rows per customer_id

Quantify the duplicate problem. Return every customer_id that appears more than once in dupes, along with the count of rows for that customer.

Sort by customer_id ascending.

Returncustomer_idcnt

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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