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N035-M1 Tier 3 · Intermediate · medium ecommerce · Brightlane

Return the `10`-character segment starting at position `5` of the order code `'ORD-2024-03-15'`

Part of String Functions (LENGTH, UPPER, LOWER, TRIM, SUBSTRING) in SQL

The problem

Brightlane's order reference system extracts the date portion from structured order codes. Each code follows the format 'ORD-YYYY-MM-DD'.

Write a query to return the 10-character segment starting at position 5 of the order code 'ORD-2024-03-15'.

Output:

  • A single row with one column, order_date, containing the extracted segment.
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
  SUBSTRING('ORD-2024-03-15', 5, 10) AS order_date

The shape

SUBSTRING('ORD-2024-03-15', 5, 10) returns the ten characters starting at position 5 of the order code, which is exactly the YYYY-MM-DD date portion after the three-character ORD- prefix. SUBSTRING is 1-indexed, so position 5 is the first character after the prefix and its leading hyphen.

Clause by clause

  • SELECT SUBSTRING('ORD-2024-03-15', 5, 10) AS order_date slices the literal and labels the result order_date. The three arguments are the source string, the start position, and the length: start at character 5 (the 2 in 2024) and take ten characters from there, which lands on the closing 5 of '15'. The result is the literal substring '2024-03-15'.
  • There is no FROM because the input is the literal itself. SUBSTRING is a scalar function that operates on one string and returns one string.

Why this and not parsing the date directly

The output spec asks for the ten-character segment, not a typed date. SUBSTRING returns text, which is what the order-reference system reads. Wrapping the result in ::date or any other cast would change the column type and overshoot what the task is asking for. When the structure is a known fixed-width prefix followed by the value, position-based extraction is the cleanest tool.

The trap

SUBSTRING is 1-indexed, not 0-indexed. A reader coming from a language where the first character is at index 0 will write SUBSTRING('ORD-2024-03-15', 4, 10) and get '-2024-03-1' with a leading hyphen and a missing final 5. The fix is the indexing convention: position 1 is the first character, position 2 is the second, and position 5 is the first character past the four-character ORD- prefix. Counting from one is the rule for every SQL string-position function in PostgreSQL.

You practiced SUBSTRING(string, start, length) with 1-indexed positions — extract a fixed-width slice from a structured code.

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