Postgres 15

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select version();

version

PostgreSQL 15.0 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-10), 64-bit

SELECT 1

CREATE TABLE test
(
  ip INET
);

CREATE TABLE

INSERT INTO test VALUES
('134.34.34.34'::INET),
('172.24.12.20'::INET);

INSERT 0 2

SELECT 
  *
FROM test
WHERE ip <<= '172.24.12/24'::INET;

ip

172.24.12.20

SELECT 1

SELECT
  ip::TEXT,
  PG_TYPEOF(ip::TEXT)
FROM test;

ip
pg_typeof

134.34.34.34/32
text

172.24.12.20/32
text

SELECT 2

SELECT
  ip
FROM test
WHERE ip::TEXT ~ '172\.24\.12\.[0-2]{1}[0-9]{1,2}'

ip

172.24.12.20

SELECT 1

SELECT
  ip
FROM test
WHERE ip::TEXT ~ '172\.24\.12\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])';

ip

172.24.12.20

SELECT 1

WITH fake_pg_stat_activity (client_addr) AS 
(
    SELECT inet '172.24.12.20'
    UNION ALL SELECT inet '192.168.0.1'
)
SELECT 
  *, 
  CASE 
    WHEN client_addr << '172.24.12/24' THEN TRUE 
    ELSE FALSE 
  END AS belongs_to_subnet
FROM fake_pg_stat_activity;

client_addr
belongs_to_subnet

172.24.12.20
t

192.168.0.1
f

SELECT 2