Your question is Identify Duplicate Records in SQL. Start with the requirements and the one table on the right.
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Bain & Company is validating client-contact intake records before loading them into its centralized analytics environment. Duplicate email addresses may represent repeated submissions and should be reviewed.
Write a PostgreSQL query to identify email addresses that occur more than once in the client_contacts table.
email is NULL, because a missing email cannot identify a duplicate contact.| Column | Type | Description |
|---|---|---|
| contact_idPK | INT | Unique contact-record identifier |
| contact_name | VARCHAR(100) | Contact's name |
| VARCHAR(255) | Contact email address used for duplicate detection | |
| source_system | VARCHAR(50) | System that submitted the record |