If you’re getting an error that reads “function mode() does not exist” in PostgreSQL, it could be that you’re using the wrong syntax with this function.

The mode() function requires a WITHIN GROUP clause, and we can get the above error if we remove that clause.

In this case, we can fix the error by adding a valid WITHIN GROUP clause.

Example of Error

Here’s an example of code that produces the error:

SELECT 
    mode()
FROM products;

Result:

function mode() does not exist

We’re told that the mode() function doesn’t exist, but we know that it does. However, it doesn’t exist with that syntax (i.e. without a WITHIN GROUP clause).

Solution

We can fix the above error by adding a valid WITHIN GROUP clause:

SELECT 
    mode() WITHIN GROUP ( ORDER BY vendorid )
FROM products;

Result:

 mode 
------
 1001

This time it ran without error.

Note that we must provide an ORDER BY clause in the WITHIN GROUP clause. Omitting the ORDER BY clause will result in another error.