Why is MySQL SUM query only returning one row?

问题

I am trying to create a MySQL query to return the sum of all statement balances for each account in my DB. The query looks like this:

SELECT SUM(balance), handle FROM statement_versions
INNER JOIN statements ON statement_versions.statement_id = statements.id
INNER JOIN accounts ON statements.account_id = accounts.id;

When I do this, it returns only one row with one summed balance and one account (account with ID 1). What I want is to return all accounts with their summed statement balance. How would I achieve this?

回答1:

You need to group by something, probably handle (I presume that is related to the account id?), otherwise MySQL will SUM all the values selected from your JOIN. Adding a GROUP BY clause makes the SUM happen for each distinct value of the column in the GROUP BY. Change your query to:

SELECT SUM(balance), handle FROM statement_versions
INNER JOIN statements ON statement_versions.statement_id = statements.id
INNER JOIN accounts ON statements.account_id = accounts.id
GROUP BY handle;

If handle is not related to accounts.id and you want to get the results grouped by accounts.id, change the query to:

SELECT SUM(balance), accounts.id FROM statement_versions
INNER JOIN statements ON statement_versions.statement_id = statements.id
INNER JOIN accounts ON statements.account_id = accounts.id
GROUP BY accounts.id;

来源：https://stackoverflow.com/questions/53019016/why-is-mysql-sum-query-only-returning-one-row