Can I Comma Delimit Multiple Rows Into One Column?

sql

string-aggregation

query-optimization

sql-techniques

byNikita Barsukov·Nov 28, 2024

Need to string together rows into a single column with commas? The STRING_AGG function will be your best buddy.

For SQL Server (2017+) and PostgreSQL:

SELECT STRING_AGG(your_column, ', ') AS combined_column
FROM your_table;

For MYSQL, GROUP_CONCAT will save your day:

SELECT GROUP_CONCAT(your_column SEPARATOR ', ') AS combined_column
FROM your_table;

Just replace your_column and your_table with your specific details. Amend ORDER BY clause to control the sequence of the concatenated elements.

Less fortunate beings, who use older versions of SQL Server, turn to the combination of STUFF and FOR XML PATH:

SELECT 
    TicketID,
    STUFF(
        (
            SELECT ',' + ISNULL(t2.ColumnName, '')
            FROM YourTable t2
            WHERE t2.TicketID = t1.TicketID
            ORDER BY t2.ColumnName
            FOR XML PATH(''), TYPE
        ).value('.', 'NVARCHAR(MAX)'), 
        1, 1, ''
    ) AS CombinedColumn
FROM YourTable t1
GROUP BY TicketID;

Making your code bulletproof

Here are additional considerations and troubleshooting tips to ensure your code runs smoothly.

Dodging NULL values

When dealing with NULL values, make sure to use the ISNULL function or similar commands. This prevents pesky disruptions in your concatenation process.

Zapping unwanted commas

Steer away from an undesired comma at the beginning of your concatenation. Careful use of SQL logic and the STUFF function will obliterate that pesky prefix.

Handling big data

For large datasets, performance is paramount. Aid your operations through indexing, batching, and partitioning data to keep your process running like a top.

Grasping every tool in your arsenal

There are plenty more techniques at your disposal to make row concatenating easier.

Oracle's unique flair

In Oracle databases, use the LISTAGG function or the SYS_CONNECT_BY_PATH to concatenate rows. Because even Oracle likes to feel special sometimes.

Tailoring your toolbox

In need for a more fitted solution? Consider custom functions or stored procedures for a tailored coalescing solution. Just remember, great power comes with great responsibility.

Vanishing duplicates

Do you want to avoid repeating yourself? Utilize the DISTINCT keyword in your subqueries. This way, you won't find yourself stuttering in SQL.

Tackling the complex

Complex problems demand complex solutions and sometimes that means temporary tables or common table expressions (CTEs) could be your saving grace. This may sound like summoning a dragon to swat a fly, but trust me, it's worth it.

Broadening your SQL horizon

When starting out, simplicity is key but as you advance your grasp on SQL, exploring in-depth techniques will pay off.

Mastering string aggregation

On the road to becoming a SQL whizz, you'll face new syntax, different data types and errors that can drive a sane developer... well, perhaps slightly less sane. It's crucial to test your queries with different datasets to ensure they are robust.

Optimizing queries

Query performance is an art and science in itself. Workout with indexes, optimize your queries, and dive into execution plans. You can even make tuning query your new hobby!