SQLAlchemy 组合查询

Question

I need to execute this SQL:

select 
    `year`, 
    `month`, 
    sum(diff) 
from 
    (select 
         `year`, `month`, 
         `readings` - LAG(`readings`) over (order by `year`) as diff 
     from table1) as summary 
group by 
    `year`, `month`

But I need to do it in SQLAlchemy.

So far I figured out 2 subqueries:

q1 = db.session.query(Table1.year, Table1.month, (Table1.readings - func.lag(Table1.readings).over(order_by=Table1.year)).label('diff'))

result = db.session.query(Table1.year, Table1.month, sum('diff')).group_by(Table1.year, Table1.month)

But I can't combine them together

Answer 1

Just turn q1 into a subquery() and select from it.

q1 = db.session.query(
        Table1.year,
        Table1.month,
        (Table1.readings - func.lag(Table1.readings).over(order_by=Table1.year)).label('diff')).\
    subquery()

result = db.session.query(q1.c.year, q1.c.month, sum(q1.c.diff)).group_by(q1.c.year, q1.c.month)