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N034-E1 Tier 3 · Intermediate · easy ecommerce · Brightlane

Return the review date for a hire on `'2024-03-15'`, computed as the hire date plus `30` days

Part of Date Arithmetic and Intervals in SQL

The problem

Brightlane's HR team schedules a probation review 30 days after each hire date.

Write a query to return the review date for a hire on '2024-03-15', computed as the hire date plus 30 days.

Output:

  • A single row with one column, review_date, containing the projected review date.
Schema · ecommerce 5 tables
categories
id integer
name text
parent_id? integer
products
id integer
name text
category_id integer
price numeric
stock_qty integer
attributes? jsonb
order_items
id integer
order_id integer
product_id integer
quantity integer
unit_price numeric
customers
id integer
name text
email text
city? text
country text
created_at timestamptz
is_active boolean
orders
id integer
customer_id integer
ordered_at timestamptz
status text
total_amount numeric
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Solution query
SELECT
  '2024-03-15'::date + INTERVAL '30 days' AS review_date

The shape

Adding INTERVAL '30 days' to a date shifts that date forward by exactly thirty calendar days and returns the resulting point in time. The expression evaluates once and produces a single dated value: the projected review date for the hire.

Clause by clause

  • SELECT '2024-03-15'::date + INTERVAL '30 days' AS review_date builds the result in two steps. The ::date cast pins the literal '2024-03-15' as a calendar date so the addition runs against the right type. Adding a fixed-day INTERVAL then advances the date thirty days, landing on April 14, 2024. The alias AS review_date names the output column to match what the HR scheduler expects.

Why INTERVAL '30 days' and not adding an integer

PostgreSQL does not let you add a raw number to a date. Writing '2024-03-15'::date + 30 reads ambiguously to the parser, since the integer could mean days, months, or something else entirely. The INTERVAL syntax names the unit explicitly, which is what date arithmetic requires. A fixed-day interval is unambiguous: thirty days is thirty days, regardless of which month the addition lands in.

You practiced date + INTERVAL '30 days' — add a fixed-day duration to a date to produce the corresponding future point in time.

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