SQL for Duplicate Customer Records | Dataford Interview Questions

Write a SQL query to identify duplicate records in a customer database.

Treat customer records as duplicates when their non-empty email addresses match after trimming surrounding whitespace and ignoring letter case. Return every record belonging to a duplicate email group.

Output

One row per duplicate customer record
Columns: record_id, full_name, email, and duplicate_count
Order by normalized email address, then record_id ascending

Schema

customer_records

Column	Type	Description
record_idPK	INT	Unique customer record identifier
full_name	VARCHAR(100)	Customer's full name
email	VARCHAR(255)	Customer email address
phone	VARCHAR(30)	Customer phone number
created_at	DATE	Date the customer record was created

Your question is SQL for Duplicate Customer Records. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

Write a SQL query to identify duplicate records in a customer database.

Output

One row per duplicate customer record
Columns: record_id, full_name, email, and duplicate_count
Order by normalized email address, then record_id ascending

Schema

customer_records

Column	Type	Description
record_idPK	INT	Unique customer record identifier
full_name	VARCHAR(100)	Customer's full name
email	VARCHAR(255)	Customer email address
phone	VARCHAR(30)	Customer phone number
created_at	DATE	Date the customer record was created

Your question is SQL for Duplicate Customer Records. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.