Unique Department Locations — DISTINCT in SQL

The problem

Helix Systems' facilities team is reviewing the company's office footprint ahead of a lease renewal decision.

Write a query to return each office location represented in the departments data, with no duplicates.

Assumptions:

The departments table contains every department at Helix Systems.
Multiple departments share the same location (e.g., several departments at headquarters), so the column has duplicates.

Output:

One row per distinct office location, with a single column location.

Schema · hr 4 tables

departments

id integer

name text

location text

budget numeric

salaries

id integer

employee_id integer

amount numeric

effective_date date

end_date? date

employees

id integer

name text

email text

department_id integer

manager_id? integer

hire_date date

title text

is_active boolean

job_history

id integer

employee_id integer

title text

department_id integer

start_date date

end_date? date

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Solution query

SELECT DISTINCT
  location
FROM
  departments

The shape

DISTINCT location collapses a column that repeats once per department down to the four cities Helix Systems actually occupies — Austin, Chicago, New York, San Francisco. The duplication is structural: many departments share a building, so the raw column carries each city as many times as it has departments in it.

Clause by clause

SELECT DISTINCT location returns the unique location values from whatever rows FROM hands up. Every department contributes its city to the candidate set, and the deduplication runs across that set to produce one row per real office.
FROM departments is the row source — the parent dimension here is location, even though the table is keyed on department. DISTINCT on a child-table column is how the parent value space gets recovered without a separate locations table.

For the lease-renewal review, the result is exactly what the facilities team needs: four rows, four cities, no inflation from departmental headcount. If a fifth city were to appear, that's the cue that the office footprint has grown since the last review.

You practiced applying DISTINCT to a column with structural duplication — many departments per location. The shape recurs whenever a one-to-many relationship is being collapsed to its parent dimension.

Return each office location represented in the departments data, with no duplicates

The shape

Clause by clause

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