SQL CONCAT

Joins two or more text values together into one — and unlike the || operator, safely treats NULL as an empty string instead of contaminating the whole result.

What & Why

CONCAT(a, b, c, ...) joins any number of values into a single string, converting non-text values (like numbers) automatically. Its standout behavior: if any input is NULL, CONCAT simply treats it as an empty string and keeps going — it doesn't propagate NULL the way most functions do.

See How It Works

BUSINESS QUESTION

Product wants to compare CONCAT with || while building feature labels from the nullable deprecated_at column.

id	name	description	team	released_at	deprecated_at
1	Activation Checklist	Guides new users through setup	growth	2024-01-20	NULL
2	CSV Export	Exports report data	platform	2024-02-14	NULL
3	Invite Nudges	Prompts workspace collaboration	growth	2024-03-05	NULL
4	Legacy Dashboard	Original reporting surface	analytics	2023-08-10	2024-06-01

Watch CONCAT and || handle the same nullable value differentlyExample 1 of 4

CONCAT(name, ' · ', deprecated_at::text) vs name || ' · ' || deprecated_at::text

id	name	deprecated_at	concat_label	operator_label
1	Activation Checklist	NULL	Activation Checklist ·	NULL
2	CSV Export	NULL	?	?
3	Invite Nudges	NULL	?	?
4	Legacy Dashboard	2024-06-01	?	?

CONCAT treats the missing date as empty text, while || propagates NULL.

EXAMPLE QUERY

SELECT
  id,
  name,
  deprecated_at,
  CONCAT(name, ' · ', deprecated_at::text) AS concat_label,
  name || ' · ' || deprecated_at::text AS operator_label
FROM product.features
ORDER BY id;

Now You Try

Practice this concept

Product compares CONCAT with || while building feature labels from nullable deprecated_at.

Available schema

product

Prefix tables with product.table_name.

idnamedeprecated_atconcat_labeloperator_label

product.features

Column	Type
id	integer
name	text
description	text
team	text
released_at	timestamp with time zone
deprecated_at	timestamp with time zone
internal_priority	integer

query.sql

Intermediate business practice