String aggregation functions concatenate multiple string values from grouped rows into a single delimited string, useful for creating lists and collections.

**Core Functions:**

PostgreSQL: STRING_AGG(column, delimiter)

MySQL: GROUP_CONCAT(column SEPARATOR delimiter)

SQL Server: STRING_AGG(column, delimiter)

**Basic Pattern:**

SELECT

category,

STRING_AGG(product_name, ', ') AS products

FROM products

GROUP BY category;

Result: "Laptop, Mouse, Keyboard" for Electronics category

**Ordering:**

STRING_AGG(column, delimiter ORDER BY sort_column)

**NULL Handling:**

- NULL values typically ignored

- Use COALESCE to replace NULL with default

Common in reporting and API responses. Used by backend engineers and data analysts to denormalize data for display and export.

Creates comma-separated lists, tag collections, and concatenated values. Essential for displaying multiple related items in single row: product tags, employee skills, order items.