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N034-M3 Tier 3 · Intermediate · medium ecommerce · Brightlane

Return the expiry date for a contract that begins on `'2024-01-15'`, computed as the start date plus `1` year and `6` months

Part of Date Arithmetic and Intervals in SQL

The problem

Brightlane's content licensing system computes contract expiry dates with a 1 year 6 month term.

Write a query to return the expiry date for a contract that begins on '2024-01-15', computed as the start date plus 1 year and 6 months.

Output:

  • A single row with one column, expiry_date, containing the resulting 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
  '2024-01-15'::date + INTERVAL '1 year 6 months' AS expiry_date

The shape

INTERVAL '1 year 6 months' is a single duration with two calendar components, and adding it to a date advances the year and the month independently. The contract starting on January 15, 2024 expires on July 15, 2025.

Clause by clause

  • SELECT '2024-01-15'::date + INTERVAL '1 year 6 months' AS expiry_date builds the expiry. The ::date cast types the literal as a calendar date. The multi-component INTERVAL literal declares both pieces of the duration in one quoted string, separated by spaces. PostgreSQL applies the year component and the month component together: one year forward from January 2024 reaches January 2025, then six more months reaches July 2025, with the day-of-month preserved throughout. The alias AS expiry_date labels the output.

Why one INTERVAL and not two additions

The two forms produce the same result. Writing '2024-01-15'::date + INTERVAL '1 year' + INTERVAL '6 months' chains two additions and lands on the same expiry. The single-literal form is more compact, names the full term as one duration, and matches how contract terms are usually expressed in the business. Either reads correctly. When the duration has a natural domain meaning, like a one-and-a-half-year term, expressing it as one literal keeps the SQL close to the spec.

You practiced multi-component INTERVAL literals like '1 year 6 months' — PostgreSQL applies each calendar component cumulatively from the source date.

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