问在Postgres中的间隔中使用可变期间

EN

startDate TIMESTAMP := endDate - ($3 || ' MONTH')::INTERVAL;

startDate TIMESTAMP := endDate - $3 * INTERVAL '1 MONTH';

CREATE OR REPLACE FUNCTION test_param(num_months integer)
  RETURNS SETOF calendar AS
$BODY$

    select * from calendar
    where cal_date <= '2008-12-31 00:00:00'
    and cal_date > date '2008-12-31' - ($1 || ' month')::interval;

$BODY$
  LANGUAGE sql VOLATILE
  COST 100
  ROWS 1000;

import pandas as pd
import sqlalchemy as sa

connection = sa.create_engine(connection_string)

df = pd.read_sql(
   sa.text('''
       select * from events
       where
       event_date between now() - (interval '1 day' * :ndays) and now()
       limit 100;
'''),
   connection,
   params={'ndays': 100}
)