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Build a display label from nullable text · SQL scenario · D8LooP

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Build a display label from nullable text

The UI shows each customer as a single line: their name, then their region in brackets. Two customers have no region yet. Return one label per customer, ordered by customer_id.

Result columns · in this order

`customer_id`	The customer.
`label`	Their display label.

How to approach it

Replace the missing value before you build the string, not after.

Sample input

shop_customersOne row per customer. region is NULL when unassigned.

customer_id	full_name	region	signed_up_on
c1	Ada Okafor	North	2025-11-02
c2	Bo Lindqvist	null	2025-12-14
c3	Chen Wei	South	2026-01-03
c4	Dara O'Neill	North	2026-01-20
c5	Eve Marsh	null	2026-02-01

5 rows — all rows shown.

Expected output

The exact result your query should return for this input.

customer_id	label
c1	Ada Okafor (North)
c2	Bo Lindqvist (unknown)
c3	Chen Wei (South)
c4	Dara O'Neill (North)
c5	Eve Marsh (unknown)

5 rows — all rows shown.

Constraints

1A customer with a region reads Ada Okafor (North).
2A customer without one reads Bo Lindqvist (unknown) — never an empty cell.
3Every customer appears; nobody is filtered out for missing a region.
4Keep the brackets and the single space exactly as shown.

Worked example

full_name || ' (' || region || ')' looks right and produces NULL for c2 and c5. Concatenation propagates NULL: joining anything to an unknown value gives an unknown result, so one missing region wipes out the entire label rather than leaving a gap in the middle of it.

What this tests

That NULL propagates through expressions rather than behaving like an empty string, and that a default has to be supplied before the value is used.

SQL

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