Listagg function: "result of string concatenation is too long"

sql

listagg

string-concatenation

performance-tips

byAlex Kataev·Feb 28, 2025

To bypass the LISTAGG constraint and prevent the "result of string concatenation is too long" error, use XMLAGG with a CLOB data type, known for its capability to manage longer strings. Divide your data into smaller chunks with ROW_NUMBER() and group by your chosen size, then concatenate using XMLAGG. Here's a snappy snippet:

WITH sliced_data AS (
  SELECT your_column, ROW_NUMBER() OVER (ORDER BY your_order_column) AS rn
  FROM your_table  --your_table is a place where magic happens
)
SELECT RTRIM(XMLAGG(XMLELEMENT(e, your_column || ',')).EXTRACT('//text()').GETCLOBVAL(), ',')
FROM sliced_data
GROUP BY trunc((rn - 1) / your_chunk_size); --divide and conquer is the motto

Substitute your_column, your_order_column, your_table, and your_chunk_size with actual column names, order of sorting, table name, and chunk size to maintain manageable string lengths.

Graceful handling of Overflows

In Oracle 12cR2 and subsequent versions, the LISTAGG function now has an ON OVERFLOW clause. It's there to save the day when your strings threaten to exceed the 4000-character limit. Here's how you wield this feature:

SELECT LISTAGG(your_column, ',') WITHIN GROUP (ORDER BY your_column) 
ON OVERFLOW TRUNCATE '...' WITH COUNT -- '...' is an infamous relic from the 90's
FROM your_table;

This will graciously and artistically trim the outputattaching '...' when the results exceed limits, and obligingly include a count of truncated values.

Power of Custom Aggregate Functions

When out-of-the-box functions don't seem to fit, tailor your own. Build a custom aggregate function. These are not your average functions as they use the mighty CLOB to handle string concatenations beyond the norm. Oracle's documentation is your one-stop-shop for guidance on mastering user-defined aggregates.

Mastering SQL Developer Settings

When flexing your muscles in SQL Developer, tweaking settings like SET LONG and SET PAGESIZE grant you power to display larger results. Beware, versions younger than 4.0 may snub results over 4000 characters.

Leveling up with XMLAGG

If LISTAGG is basic training, XMLAGG is the advanced course. Kickstart your journey with:

SELECT RTRIM(XMLAGG(XMLELEMENT(e, your_column || ',') ORDER BY your_order_column).EXTRACT('//text()').GETCLOBVAL(), ',') 
FROM your_table;  --welcome to Hogwarts of DATA

This syntax is an elegant dancer, gracefully ordering rows and nipping off trailing commas. Thus, you achieve a neatly concatenated string with values in perfect order and format.

Battleplan against ORA-01489

Combatting ORA-01489? It's a sly villain pronouncing your string concatenation results too big. XMLAGG is the superhero here, along with accomplices like dividing your queries, or even contemplating a schema makeover if the villain appears too often.

Enhancing performance for large datasets

For massive datasets, slicing data into logical, bite-sized portions before deploying LISTAGG could fend off overflow errors. Think of your data in terms of dates, categories, or event types, to get a series of manageable strings.

List of considerations and performance tips

Performance tends to dip with large datasets or complex queries, especially without proper indexing.
Subqueries might be a handy alternative to break down data and prevent overloads.
Timely database maintenance, like purging old records, can help prevent string aggregation from growing too long.
Keeping a close eye on long-running queries and adjusting them accordingly keeps your database fit and fast.