LISTAGG in Oracle - Examples & AI Generator

The LISTAGG function in Oracle lets you transform values from multiple rows into a single, delimited string—ideal for generating quick reports or summaries. But, the exact Oracle LISTAGG syntax can be tricky, especially across evolving database versions or when dealing with partitioning and ordering.

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LISTAGG Syntax in Oracle

Basic Syntax

LISTAGG ( expression [, delimiter ] ) WITHIN GROUP (ORDER BY order_item)
[OVER (PARTITION BY partition_expression)]

• expression: The column to concatenate

• delimiter: Optional separator (default is no separator)

• WITHIN GROUP (ORDER BY ...): Specifies ordering of concatenated items

• OVER (PARTITION BY ...): Optional, for aggregation within partitions (since 12c)

Common Oracle-specific considerations:

• Order of concatenated results determined by the ORDER BY clause inside WITHIN GROUP

• Oracle raises an error if the result exceeds 4000 bytes (pre-19c)

LISTAGG Examples You Can Generate Instantly

1. Customer Orders as a Comma-Separated List

SELECT customer_id,
       LISTAGG(order_id, ', ') WITHIN GROUP (ORDER BY order_id) AS orders
FROM orders
GROUP BY customer_id;

Business scenario: See all order IDs for each customer in a single row for better reporting.

2. Product Names Grouped by Category

SELECT category,
       LISTAGG(product_name, '; ') WITHIN GROUP (ORDER BY product_name) AS all_products
FROM products
GROUP BY category;

Business scenario: Display all products per category, sorted alphabetically and separated by semicolons for dashboard exports.

3. Employees Listed by Department (Oracle 12c+ Partitioned)

SELECT department_id,
       employee_id,
       LISTAGG(project_name, ', ') WITHIN GROUP (ORDER BY project_name)
          OVER (PARTITION BY department_id) AS projects
FROM employee_projects;

Business scenario: Each employee sees all projects in their department as a single string, leveraging Oracle partitioning for advanced analytics.

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Frequently Asked Questions

• Q: What happens if LISTAGG output exceeds 4000 bytes in Oracle?
  A: Prior to Oracle 19c, LISTAGG throws an error on overflow. From 19c, you can use the ON OVERFLOW clause to handle overflow gracefully.

• Q: Can I use DISTINCT inside LISTAGG in Oracle?
  A: Oracle doesn’t support LISTAGG(DISTINCT ...) directly. As a workaround, use a subquery to SELECT DISTINCT values first.

• Q: How is LISTAGG different in Oracle compared to SQL Server?
  A: Oracle uses LISTAGG ... WITHIN GROUP (ORDER BY ...), while SQL Server commonly uses STRING_AGG() with slightly different syntax. Use AI2sql to switch between databases instantly.

Conclusion

The LISTAGG function in Oracle is powerful but demands strict attention to syntax, ordering, and overflow scenarios. Rather than memorizing or troubleshooting Oracle LISTAGG syntax, use AI2sql for instant, accurate, and business-ready SQL—no coding required, in just 10 seconds.

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