aggregate

STRING_AGG()

Concatenates values from a group into a single string, separated by a delimiter.

Description

STRING_AGG is an aggregate function that gathers values from a group and joins them into one string, with a separator between each value. It's the group-aware cousin of CONCAT — perfect for turning a list of names into a comma-separated string per department.

Syntax

STRING_AGG(expression, separator)
STRING_AGG(DISTINCT expression, separator)

Parameters

Name	Description	Optional
expression	The value to concatenate (usually a column).	No
separator	The delimiter inserted between values.	No

Return Type

Returns a VARCHAR containing all grouped values joined by the separator. If the group is empty it returns NULL.

Examples

Employees & Departments

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Employees & Departments

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Order the values

To control the order of items in the result, use the ORDER BY clause inside the function: STRING_AGG(first_name ORDER BY first_name, ', ').

Common Mistakes

Forgetting GROUP BY. Without a grouping, STRING_AGG collapses every row into a single string.
Assuming a fixed order. The order of concatenated values isn't guaranteed unless you use ORDER BY inside the call.
Mixing with NULLs. NULL values in the group are skipped, not rendered as empty slots.

Related functions

CONCAT()

string

Joins two or more strings together into a single string.