3 sposoby sprawdzenia typu danych kolumny w PostgreSQL

Oto trzy sposoby uzyskania typu danych danej kolumny w MariaDB.

\d Polecenie

W psql \d Polecenie wyświetla informacje o tabelach, widokach, widokach zmaterializowanych, indeksie, sekwencjach lub tabelach obcych.

Możemy użyć tego polecenia, aby sprawdzić typ danych kolumn w danej tabeli:

\d public.actor

Wynik:

                                             Table "public.actor"
+-------------+-----------------------------+-----------+----------+-----------------------------------------+
|   Column    |            Type             | Collation | Nullable |                 Default                 |
+-------------+-----------------------------+-----------+----------+-----------------------------------------+
| actor_id    | integer                     |           | not null | nextval('actor_actor_id_seq'::regclass) |
| first_name  | character varying(45)       |           | not null |                                         |
| last_name   | character varying(45)       |           | not null |                                         |
| last_update | timestamp without time zone |           | not null | now()                                   |
+-------------+-----------------------------+-----------+----------+-----------------------------------------+
Indexes:
    "actor_pkey" PRIMARY KEY, btree (actor_id)
    "idx_actor_last_name" btree (last_name)
Referenced by:
    TABLE "film_actor" CONSTRAINT "film_actor_actor_id_fkey" FOREIGN KEY (actor_id) REFERENCES actor(actor_id) ON UPDATE CASCADE ON DELETE RESTRICT
Triggers:
    last_updated BEFORE UPDATE ON actor FOR EACH ROW EXECUTE FUNCTION last_updated()

Możemy dodać znak plus (+ ) aby ujawnić rozszerzone informacje:

\d+ public.actor

Wynik:

                                                                 Table "public.actor"
+-------------+-----------------------------+-----------+----------+-----------------------------------------+----------+--------------+-------------+
|   Column    |            Type             | Collation | Nullable |                 Default                 | Storage  | Stats target | Description |
+-------------+-----------------------------+-----------+----------+-----------------------------------------+----------+--------------+-------------+
| actor_id    | integer                     |           | not null | nextval('actor_actor_id_seq'::regclass) | plain    |              |             |
| first_name  | character varying(45)       |           | not null |                                         | extended |              |             |
| last_name   | character varying(45)       |           | not null |                                         | extended |              |             |
| last_update | timestamp without time zone |           | not null | now()                                   | plain    |              |             |
+-------------+-----------------------------+-----------+----------+-----------------------------------------+----------+--------------+-------------+
Indexes:
    "actor_pkey" PRIMARY KEY, btree (actor_id)
    "idx_actor_last_name" btree (last_name)
Referenced by:
    TABLE "film_actor" CONSTRAINT "film_actor_actor_id_fkey" FOREIGN KEY (actor_id) REFERENCES actor(actor_id) ON UPDATE CASCADE ON DELETE RESTRICT
Triggers:
    last_updated BEFORE UPDATE ON actor FOR EACH ROW EXECUTE FUNCTION last_updated()
Access method: heap

Kolumny information_schema.columns Zobacz

Kolumny information_schema.columns widok zawiera informacje o kolumnach:

SELECT
    column_name,
    data_type,
    character_maximum_length AS max_length,
    character_octet_length AS octet_length
FROM
    information_schema.columns
WHERE
    table_schema = 'public' AND 
    table_name = 'actor' AND
    column_name = 'first_name';

Wynik:

+-------------+-------------------+------------+--------------+
| column_name |     data_type     | max_length | octet_length |
+-------------+-------------------+------------+--------------+
| first_name  | character varying |         45 |          180 |
+-------------+-------------------+------------+--------------+

pg_typeof() Funkcja

pg_typeof() funkcja zwraca OID typu danych wartości, która jest do niej przekazywana.

Możemy zatem użyć go, aby uzyskać typ danych kolumny, przekazując kolumnę do pg_typeof() funkcja podczas odpytywania tabeli:

SELECT pg_typeof(first_name)
FROM public.actor
LIMIT 1;

Wynik:

+-------------------+
|     pg_typeof     |
+-------------------+
| character varying |
+-------------------+

W PostgreSQL, character varying to nazwa dla varchar (właściwie varchar jest aliasem character varying ).