3 manieren om het gegevenstype van een kolom in PostgreSQL te controleren

Hier zijn drie manieren om het gegevenstype van een bepaalde kolom in MariaDB te krijgen.

De \d Commando

In psql, de \d commando toont informatie over tabellen, weergaven, gerealiseerde weergaven, index, reeksen of vreemde tabellen.

We kunnen dit commando gebruiken om het gegevenstype van de kolommen in een bepaalde tabel te controleren:

\d public.actor

Resultaat:

                                             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()

We kunnen een plusteken toevoegen (+ ) om uitgebreide informatie te onthullen:

\d+ public.actor

Resultaat:

                                                                 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

De information_schema.columns Bekijk

De information_schema.columns weergave bevat informatie over kolommen:

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';

Resultaat:

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

De pg_typeof() Functie

De pg_typeof() functie retourneert de OID van het gegevenstype van de waarde die eraan wordt doorgegeven.

We kunnen het daarom gebruiken om het gegevenstype van een kolom te krijgen door de kolom door te geven aan de pg_typeof() functie tijdens het opvragen van de tabel:

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

Resultaat:

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

In PostgreSQL, character varying is de naam voor varchar (eigenlijk varchar is de alias voor character varying ).