checking_sizes.sql

psql> create table t(a uuid, b text, c char(36));
CREATE TABLE

psql> insert into t values (gen_random_uuid(), 'some amount of text', 'some amount of text');
INSERT 0 1
                              
psql> select pg_column_size(a), pg_column_size(b), pg_column_size(c) from t;
 pg_column_size | pg_column_size | pg_column_size
----------------+----------------+----------------
             16 |             20 |             37

psql> insert into t values (gen_random_uuid(), gen_random_uuid(), gen_random_uuid());
INSERT 0 1

psql> select * from t;
                  a                   |                  b                   |                  c
--------------------------------------+--------------------------------------+--------------------------------------
 1cbf80ed-a309-4163-8231-c5431e438500 | some amount of text                  | some amount of text
 2a44f391-1e9d-4b0a-a15f-f7f12eb15cfc | 8daed507-a4f4-4b05-a3e6-dc3ac49856bf | 12355217-df08-481d-8c1c-20d6b36c60a0
(2 rows)

psql> select pg_column_size(a), pg_column_size(b), pg_column_size(c) from t;
 pg_column_size | pg_column_size | pg_column_size
----------------+----------------+----------------
             16 |             20 |             37
             16 |             37 |             37