Postgres 13

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CREATE OR REPLACE FUNCTION get_id()
RETURNS varchar
language plpgsql
AS $$
BEGIN
 RETURN (SELECT 'IP-' || (SELECT count(1) from city) + 1);
END;
$$;

CREATE FUNCTION


CREATE TABLE city (
id varchar(255) DEFAULT get_id() NOT NULL,
name varchar (255) NOT NULL
);

CREATE TABLE


INSERT INTO city (name) VALUES ('SURAT'),('PUNE'),('MUMBAI');

INSERT 0 3


SELECT * FROM city;


id
name


IP-1
SURAT

IP-2
PUNE

IP-3
MUMBAI



SELECT 3