Some RDBMSs have a GROUP_CONCAT() function that allows you to return a query column as a delimited list (for example, a comma separated list). MySQL and MariaDB are two that have such a function.

PostgreSQL and SQL Server have similar functions called STRING_AGG().

Oracle, on the other hand, has the LISTAGG() function that does pretty much the same thing (and perhaps more).

So you could say that LISTAGG() is Oracle’s GROUP_CONCAT() equivalent.

Example

Here’s a basic example to demonstrate how Oracle’s LISTAGG() function works:

SELECT LISTAGG(region_name, ',') 
FROM regions;

Result:

                      LISTAGG(REGION_NAME,',') 
______________________________________________ 
Europe,Americas,Asia,Middle East and Africa   

In this case, I specified that the separator is a comma.

Here’s what happens when we just do the query without the LISTAGG() function:

SELECT region_name 
FROM regions;

Result:

              REGION_NAME 
_________________________ 
Europe                    
Americas                  
Asia                      
Middle East and Africa  

We get four rows, each with a separate value, instead of one comma separated row that contains all values.

The LISTAGG() function also enables us to order the results, return only unique values (via the DISTINCT clause), and more.

See LISTAGG() Function in Oracle for more examples.