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N035-M3 Tier 3 · Intermediate · medium ecommerce · Brightlane

Return the value of `'000042'` after every leading `'0'` character is removed

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

The problem

Brightlane's data pipeline strips leading zeros from account numbers before loading them into a reporting system.

Write a query to return the value of '000042' after every leading '0' character is removed.

Output:

  • A single row with one column, account_number, containing the stripped value.
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
  TRIM(
    LEADING '0'
    FROM
      '000042'
  ) AS account_number

The shape

TRIM(LEADING '0' FROM '000042') walks the left side of the string and removes every '0' character it encounters until it hits a non-'0', at which point it stops. The four leading zeros are stripped and the result is the string '42', which is the form the reporting system loads.

Clause by clause

  • SELECT TRIM(LEADING '0' FROM '000042') AS account_number runs the directional TRIM against the literal and labels the result account_number. The LEADING keyword tells TRIM to operate only on the left end of the string; the '0' is the character to strip. Each leading '0' is removed one by one until the function reaches the '4', which is not a '0', so the function stops and returns what remains.
  • There is no FROM because the value being stripped is the literal in the SELECT. The function takes one input and returns one output.

Why this and not the default both-sides TRIM

A plain TRIM('0' FROM '000042') would strip from both ends, and since the string ends in '2' rather than '0', the right-side pass would do nothing on this specific input and the result would be the same '42'. The LEADING keyword is still load-bearing for the pipeline. An account number like '01020' would lose its trailing '0' under a both-sides strip, which would silently corrupt the value. LEADING makes the directional intent explicit and keeps the behavior correct for every input the pipeline will see.

You practiced TRIM(LEADING 'char' FROM ...) — strip a specific character only from the left side, preserving the right side intact.

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