Question

When I add an aggregate function to the SQL query, I get a row of empty values returned. If I take the aggregate function out, I get no rows returned. Why is this? If there is nothing to return, I don’t want a row. In my schema, each envelope can have many transactions. Here is an example of what I’m seeing:

sqlite> SELECT envelopes.*, SUM(transactions.amount) FROM envelopes LEFT OUTER JOIN transactions ON transactions.envelope_id = envelopes.id WHERE envelopes.user_id = 1;
id          name        user_id     income      unassigned  parent_envelope_id  expense     created_at  updated_at  SUM(transactions.amount)
----------  ----------  ----------  ----------  ----------  ------------------  ----------  ----------  ----------  ------------------------

sqlite> SELECT envelopes.* FROM envelopes LEFT OUTER JOIN transactions ON transactions.envelope_id = envelopes.id WHERE envelopes.user_id = 1;
sqlite> select sqlite_version();
sqlite_version()
----------------
3.7.5           
sqlite>

I would love to know how to use the SUM() function and still get no row returned when there is no information. I tried grouping by all the columns in the envelopes table and that seemed to fix it, but I’d rather not group if I don’t have to.

Answer 1

You don’t need to group on every column. You just need to group on envelopes.ID and then join to get the remaining columns. Try this query instead:

SELECT
    envelopes.id,
    envelopes.col2,
    ...
    envelopes.coln,
    totals.total
FROM envelopes
JOIN
(
    SELECT envelopes.id, SUM(transactions.amount) AS total
    FROM envelopes
    LEFT OUTER JOIN transactions
    ON transactions.envelope_id = envelopes.id
    WHERE envelopes.user_id = 1
    GROUP BY envelopes.id
) AS totals
ON totals.id = envelopes.id