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N012-H1 Tier 1 · Foundations · hard ecommerce · Brightlane

Return the name of every product that qualifies

Part of BETWEEN, IN, and LIKE in SQL

The problem

Brightlane's discount programme applies to standard Apex Titan models only. A qualifying model has a name that starts with Apex Titan 1 and is followed by exactly one additional character — not zero, not two.

Write a query to return the name of every product that qualifies.

Assumptions:

  • The products table contains every product in Brightlane's catalogue.
  • The catalogue contains names like Apex Titan 1, Apex Titan 13, Apex Titan 15, and Apex Titan 15 Pro — only the ones with exactly one trailing character (e.g., Apex Titan 13) qualify.

Output:

  • One row per qualifying product, with a single column name.
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
  name
FROM
  products
WHERE
  name LIKE 'Apex Titan 1_'

The shape

The trailing _ is the load-bearing piece. LIKE 'Apex Titan 1_' matches the literal prefix Apex Titan 1 followed by exactly one additional character — not zero, not two — which is what the discount programme's eligibility rule needs.

Clause by clause

  • SELECT name returns the single column the eligibility report needs: the product label, so the team can see which Apex Titan models qualify.
  • FROM products reads the catalogue.
  • WHERE name LIKE 'Apex Titan 1_' keeps only the rows whose name matches the pattern character-for-character: the literal Apex Titan 1, then any single character. Apex Titan 15 matches because 5 fills the _ slot. Apex Titan 1 is rejected because there's nothing after the 1 and _ requires exactly one character. Apex Titan 15 Pro is rejected because the _ only accepts one character and the name continues for several more after the 5.

Why this and not LIKE 'Apex Titan 1%'

The two wildcards encode different rules. _ matches exactly one character; % matches zero or more. They're not interchangeable — they answer different questions.

LIKE 'Apex Titan 1%' would let Apex Titan 1, Apex Titan 13, Apex Titan 15, and Apex Titan 15 Pro all through. The % absorbs whatever comes after the 1, including nothing at all. That's the wrong filter for the discount programme, which is restricted to standard models — a name with a Pro suffix or no trailing digit shouldn't qualify.

The choice between _ and % is precision versus open-ended length. Use _ when the count of remaining characters is fixed and known. Use % when the tail can be any length, including empty.

The trap

Reach for % by default and the eligibility rule gets quietly widened. The query runs, returns a plausible-looking list, and the discount applies to models that were never supposed to qualify. The fix is to read the rule literally: "exactly one additional character" is _, full stop. The same reasoning extends to multi-character fixed-length matches — '__' for two characters, '___' for three. Each underscore is one character, no more and no less.

You practiced matching exactly one character with the _ wildcard. The recurring choice between _ and % is precision vs. open-ended length.

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