Departments with More Than Five Employees

The problem

Helix Systems' HR director is reviewing departmental capacity to identify teams that may need additional headcount.

Write a query to return the department ID and employee count for every department with more than five employees.

Assumptions:

The employees table contains every active and former employee at Helix Systems.
department_id links each employee to their department.
The threshold is on the per-department headcount.

Output:

One row per qualifying department, with columns department_id and employee_count.

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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Worked solution Try it yourself first

Solution query

SELECT
  department_id,
  COUNT(*) AS employee_count
FROM
  employees
GROUP BY
  department_id
HAVING
  COUNT(*) > 5

The shape

The headcount-by-department report comes from grouping employees on department_id and counting the rows in each group. HAVING COUNT(*) > 5 keeps only the departments large enough for the HR director's review — department 1 with 17 employees, 3 with 11, 2 with 7, and the two six-person teams.

Clause by clause

SELECT department_id, COUNT(*) AS employee_count returns the grouping column with its per-group row count. COUNT(*) here means "every employee that landed in this department's group" — column values are not consulted, only row existence.
FROM employees is the source set: every active and former Helix Systems employee.
GROUP BY department_id partitions the rows into one group per department. The working set after this clause has one row per distinct department_id.
HAVING COUNT(*) > 5 filters those department rows by their headcount. Departments with five or fewer employees drop out; six or more survive.

Why this and not `WHERE COUNT(*) > 5`

The per-group count doesn't exist until GROUP BY has finished partitioning. WHERE runs earlier, when the only thing in scope is a single employee row. There is no count to compare against at that stage. HAVING is the only clause that runs after grouping, which makes it the only place a COUNT(*) threshold can be checked.

You practiced the canonical GROUP BY + HAVING shape against a count threshold. Any "groups with at least N members" question takes this exact form — GROUP BY builds the groups, HAVING COUNT(*) > N filters them.

Return the department ID and employee count for every department with more than five employees

The shape

Clause by clause

Why this and not `WHERE COUNT(*) > 5`

Reading explains SQL. Writing it, over and over with instant feedback, is what makes you fluent.

The shape

Clause by clause

Why this and not WHERE COUNT(*) > 5

Reading explains SQL. Writing it, over and over with instant feedback, is what makes you fluent.

Why this and not `WHERE COUNT(*) > 5`