Melkij

/**
 * Clerk
 *
 * @Table(schema="schema")
 */
class Clerk { }

create sequence serial_number_seq minvalue 1 maxvalue 999999999;

select admin_id
count(*) filter(where created_at >= '2019-01-01' and created_at < '2019-02-01'),
count(*) filter(where created_at >= '2019-02-01' and created_at < '2019-03-01'),
....
from tablename where ... group by admin_id

melkij=> create table identity_test (i int primary key generated by default as identity, val int);
CREATE TABLE
melkij=> insert into identity_test (val) values (1);
INSERT 0 1
melkij=> table identity_test;
 i | val 
---+-----
 1 |   1
(1 строка)

melkij=> create table identity_test_like (like identity_test INCLUDING COMMENTS INCLUDING CONSTRAINTS INCLUDING DEFAULTS INCLUDING INDEXES);
CREATE TABLE
melkij=> \d identity_test_like
                    Таблица "public.identity_test_like"
 Столбец |   Тип   | Правило сортировки | Допустимость NULL | По умолчанию 
---------+---------+--------------------+-------------------+--------------
 i       | integer |                    | not null          | 
 val     | integer |                    |                   | 
Индексы:
    "identity_test_like_pkey" PRIMARY KEY, btree (i)

melkij=> \d identity_test
                                Таблица "public.identity_test"
 Столбец |   Тип   | Правило сортировки | Допустимость NULL |           По умолчанию           
---------+---------+--------------------+-------------------+----------------------------------
 i       | integer |                    | not null          | generated by default as identity
 val     | integer |                    |                   | 
Индексы:
    "identity_test_pkey" PRIMARY KEY, btree (i)