Duplicate Records

Source data — Pattern 11: Interview SQL Patterns

All queries run against the shared employees table (see schema.sql). Topics 71 and 72 introduce an orders table to solve consecutive records and gaps-and-islands problems. Topics 73 and 74 introduce a monthly_sales table to demonstrate PIVOT and UNPIVOT operations.

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What it does

Groups rows to identify duplicate values.

Problem

Find duplicate email addresses.

SELECT email,COUNT(*)
FROM employees
GROUP BY email
HAVING COUNT(*)>1;

Result