Re: MySQL 8 is not using INDEX when subquery has a group column

[Peter Brawley]

In the query ...

explain 
update accounts a 
join (
  select uid, sum(balance) balance, day(current_date()) day 
  from users
) r on r.uid=a.uid and r.day=a.day 
set a.balance=r.balance;

... the subquery is missing a Group By clause. Once that's supplied, Explain shows index use.