Finding Missing Numbers in SQL | Dataford Interview Questions

Business Context

Ernst & Young U.S. LLP uses employee-number sequences to identify gaps in HR data loads. A missing number may indicate an incomplete extract or a record that requires investigation.

Task

Write a PostgreSQL query that identifies every missing empnum in the expected inclusive sequence from 1001 through 1015.

Requirements

Generate every expected employee number in the specified range, including the boundary values.
Return only sequence values that do not appear in emp.
Ignore duplicate employee numbers and NULL values in the source table.
Return one column named missing_empnum, sorted in ascending order.

Schema

emp

Column	Type	Description
emp_idPK	INTEGER	Unique row identifier
empnum	INTEGER	Employee number, which may contain duplicates or NULL
employee_name	VARCHAR(100)	Employee name when available

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