PostgreSQL create table statement: auto insert id - sql

Question

I am using PostgreSQL 14. For tenant system, My script
DROP TABLE IF EXISTS tenant;
CREATE TABLE tenant
(
id smallserial primary key,
company_tax_code character varying(14),
period character varying(16), -- 2021070420220705
created timestamp with time zone
);
DROP TABLE IF EXISTS account_default;
CREATE TABLE account_default
(
id smallint,
ref_type smallint not null,
ref_type_name character varying(256),
voucher_type smallint not null,
column_name character varying(64) not null,
column_caption character varying(128) not null,
filter_condition character varying(1024),
default_value character varying(32),
sort_order smallint,
created timestamp with time zone,
created_by character varying(64),
modified timestamp with time zone,
modified_by character varying(64),
tenant_id smallint,
PRIMARY KEY (id, tenant_id),
CONSTRAINT fk_tenant FOREIGN KEY (tenant_id) REFERENCES tenant (id)
);
I am looking something like
DROP TABLE IF EXISTS account_default;
CREATE TABLE account_default
(
id smallint default value (max_value of account_default.id + 1 where tenant_id = account_default.tenant_id,
ref_type smallint not null,
ref_type_name character varying(256),
voucher_type smallint not null,
column_name character varying(64) not null,
column_caption character varying(128) not null,
filter_condition character varying(1024),
default_value character varying(32),
sort_order smallint,
created timestamp with time zone,
created_by character varying(64),
modified timestamp with time zone,
modified_by character varying(64),
tenant_id smallint,
PRIMARY KEY (id, tenant_id),
CONSTRAINT fk_tenant FOREIGN KEY (tenant_id) REFERENCES tenant (id)
);
Help me
DROP TABLE IF EXISTS account_default;
CREATE TABLE account_default
(
id smallint default value (max_value of account_default.id + 1 where tenant_id = account_default.tenant_id
I need composite key
(table_id, tenant_id)
(1, 1)
(2, 1)
(3, 1)
(1, 2)
(2, 2)
(1, 3)
If insert, I need
(4, 1)
explain
4 = (max (table_id) where tenant_id = 1) + 1;
insert like tirgger or automation at database-side.

Answer 1

demo
changed all the character varying to text data type.
changed small int to bigint data type.
removed some not null constraint.
the cost is figure out the new tenant id in the current table account_default or not.
function and trigger.
CREATE OR REPLACE FUNCTION restart_seq ()
RETURNS TRIGGER
AS $$
BEGIN
RAISE NOTICE 'new.tenant_id: %', NEW.tenant_id;
RAISE NOTICE 'all.tenant_id: %', (
SELECT
array_agg(tenant_id)
FROM
tenant);
RAISE NOTICE 'new.tenant_id in : %', (
SELECT
NEW.tenant_id IN (
SELECT
tenant_id
FROM
tenant));
IF (NEW.tenant_id NOT IN (
SELECT
tenant_id
FROM
account_default)) THEN
NEW.acc_id = 1;
ALTER SEQUENCE account_default_acc_id_seq
RESTART WITH 2;
RAISE NOTICE 'currval(''account_default_acc_id_seq''): %', currval('account_default_acc_id_seq');
END IF;
RETURN new;
END;
$$
LANGUAGE plpgsql;
create or replace trigger trg_reset_the_accid
before insert on account_default
for each row execute procedure restart_seq();