Question

The time is not sorted inside aggregate function in this query:

SELECT id,
       aggregate(time)
FROM   (SELECT *
        FROM   TABLE
        ORDER  BY time) AS foo
GROUP  BY something; 

How can I sort by column inside group by expression?

Answer 1

You shouldn’t have an ORDER BY on a subquery and you don’t need it.

You can add an ORDER BY to the result of the aggregate function, but that won’t affect how the aggregate function calculates its results.

If you want to affect the order in which the aggregate function looks at its arguments then you can can add an ORDER BY to the aggregate function but only in some databases and in some situations.

SELECT id, aggregate(time ORDER BY time)
FROM   (SELECT *  FROM   TABLE) AS foo
GROUP  BY something; 

Examples

• PostgreSQL
• MySQL’s GROUP_CONCAT