用不同的where子句组合/合并两个查询

Question

我有以下有效的查询。它包括billing.transaction表中所有状态的交易总数。我需要添加另一列（第4列），其中具有特定状态（例如“有效”）的交易量，以计算每个城市中具有“有效”状态的交易总额与t_amount的比率。感谢您的支持。

先谢谢您。

`select left(t.reference_id,5) as city_code,
   case when left(t.reference_id,5) = 'DE-01' then 'city1'
        when left(t.reference_id,5) = 'DE-02' then 'city2'
        when left(t.reference_id,5) = 'DE-03' then 'city3'
        when left(t.reference_id,5) = 'DE-04' then 'city4'
        when left(t.reference_id,5) = 'DE-05' then 'city5'
        when left(t.reference_id,5) = 'DE-09' then 'city6'
        when left(t.reference_id,5) = 'DE-11' then 'city7'
        else 'city8'
        end as city,
   sum(e.amount) as t_amount
from billing.transaction_entry e
left join billing.transaction t on e.transaction_id = t.id
where e.amount > '0' and t.created_at > '2019-06-30' and t.created_at <  
'2019-08-01' and t.type='MONTHLY_RENT'
group by left(t.reference_id,5)
order by t_amount desc;`