Postgres 13

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CREATE TABLE cars(
    id serial PRIMARY KEY,  
    make varchar(32) not null,
    model varchar(32),
    has_automatic_transmission boolean not null default false,
    created_on_date timestamptz not null DEFAULT NOW()
);
SELECT pg_get_expr(d.adbin, d.adrelid) -- default_value
FROM   pg_catalog.pg_attribute a
JOIN   pg_catalog.pg_attrdef   d ON (d.adrelid, d.adnum) = (a.attrelid, a.attnum) 
WHERE  a.attrelid = 'public.cars'::regclass
AND    a.attname  = 'has_automatic_transmission';


pg_get_expr


false


SELECT pg_get_expr(d.adbin, d.adrelid) -- default_value
FROM   pg_catalog.pg_attribute a
JOIN   pg_catalog.pg_attrdef   d ON (d.adrelid, d.adnum) = (a.attrelid, a.attnum) 
WHERE  a.attrelid = 'public.cars'::regclass
AND    a.attname  = 'created_on_date';


pg_get_expr


now()


CREATE OR REPLACE FUNCTION cars_insert (make_in text
                                      , model_in text
                                      , has_automatic_transmission_in boolean
                                      , created_on_date_in timestamptz)  
  RETURNS public.cars AS
$func$
INSERT INTO cars(make, model, has_automatic_transmission, created_on_date) 
VALUES (make_in
      , model_in
      , COALESCE(has_automatic_transmission_in
               , (SELECT pg_get_expr(d.adbin, d.adrelid)::bool -- default_value
                  FROM   pg_catalog.pg_attribute a
                  JOIN   pg_catalog.pg_attrdef   d ON (d.adrelid, d.adnum) = (a.attrelid, a.attnum) 
                  WHERE  a.attrelid = 'public.cars'::regclass
                  AND    a.attname  = 'has_automatic_transmission'))
      , COALESCE(created_on_date_in
               , (SELECT pg_get_expr(d.adbin, d.adrelid)::timestamptz -- default_value
                  FROM   pg_catalog.pg_attribute a
                  JOIN   pg_catalog.pg_attrdef   d ON (d.adrelid, d.adnum) = (a.attrelid, a.attnum) 
                  WHERE  a.attrelid = 'public.cars'::regclass
                  AND    a.attname  = 'created_on_date'))
       )
RETURNING *;
$func$
LANGUAGE sql;
SELECT * FROM cars_insert('foo_make', 'foo_model', NULL, NULL);


id
make
model
has_automatic_transmission
created_on_date


1
foo_make
foo_model
f
2022-02-25 10:23:32.364987+00