users(user_id, city) and trades(trade_id, user_id, status, amount)

Return the top three cities by number of completed trades, as city and completed_trade_count. Most trades first; break ties by city alphabetically.

status holds other values besides 'completed', and they must not be counted.

Tables

trades

trade_id  user_id  status     amount
--------  -------  ---------  ------
1         1        completed  10.00
2         1        completed  20.00
3         2        completed  30.00
4         3        completed  40.00
5         3        completed  50.00
6         4        completed  60.00
7         4        completed  70.00
8         5        completed  80.00
... 3 more row(s)

users

user_id  city
-------  ------
1        Lagos
2        Lagos
3        Oslo
4        Cairo
5        Boston

Expected result

city   completed_trade_count
-----  ---------------------
Lagos  3
Cairo  2
Oslo   2