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N035-M4 Tier 3 · Intermediate · medium ecommerce · Brightlane

Return everything from position `9` onward in the string `'ERROR: Connection refused'`

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

The problem

Brightlane's logging system extracts the message body from log entries that begin with a fixed 8-character prefix.

Write a query to return everything from position 9 onward in the string 'ERROR: Connection refused'.

Output:

  • A single row with one column, message_body, containing the suffix from position 9 to the end of the string.
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('ERROR:  Connection refused', 9) AS message_body

The shape

SUBSTRING('ERROR: Connection refused', 9) returns everything from position 9 to the end of the string. With no third argument, SUBSTRING takes the source from the start position onward instead of slicing a fixed-width window, which is exactly what extracting a variable-length message body needs.

Clause by clause

  • SELECT SUBSTRING('ERROR: Connection refused', 9) AS message_body extracts the suffix and labels it message_body. The two-argument form is the source string and the start position: position 1 is the E of ERROR, position 7 is the colon, positions 7 and 8 are the two spaces in the prefix, and position 9 is the C of Connection. The function returns every character from there to the final d, which is the message body 'Connection refused'.
  • There is no FROM because the source is the literal in the SELECT. The function operates on one input and returns one output.

Why omit the length

The message body has no fixed width. 'Connection refused' is 18 characters; another log entry might carry 'Disk full' at 9 characters or a long stack trace at hundreds. Passing a specific length to SUBSTRING would either truncate the longer messages or trail spaces on the shorter ones. The two-argument form takes everything to the end of the string by definition, which is the only shape that handles every input correctly.

You practiced SUBSTRING(string, start) without a length — return everything from the start position to the end of the string.

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