Как выбрать один и тот же столбец дважды в другом формате в Postgres Sql?

Question

Я хочу фактическое значение столбца вместе с усеченным значением столбца, как показано ниже.может любой может помочь.

Select "sub1"."TimestampField","month_trunc1","month_trunc2" 
from (
   Select  "Id", date_trunc('month', "TimestampField") as "month_trunc1", "TimestampField" 
   from "Table"
) as "sub1", (
  Select  "Id", date_trunc('month', "TimestampField") as "month_trunc2", "TimestampField" 
  from "Table"
) as "sub2" 
WHERE "month_trunc2" = ("month_trunc1"+interval '1 month');

Answer 1

Вы можете упростить свой пример, используя JOIN для той же таблицы:

 SELSECT 
   "sub1"."mainfield",
   "sub1"."TimestampField" as month1, 
   "sub2"."TimestampField" as month2, 
   date_trunc('month', "sub1"."TimestampField") as "month_trunc1", 
   date_trunc('month', "sub2"."TimestampField") as "month_trunc2"
 FROM "Table" "sub1" 
 JOIN "Table" "sub2"
       ON "month_trunc2" = ("month_trunc1"+interval '1 month');