PostgreSQL

postgres=> \c mario_database

SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
You are now connected to database "mario_database" as user "freecodecamp".
mario_database=> DROP DATABASE second_database

\l
mario_database=> \l
mario_database=>                                    List of databases
+----------------+--------------+----------+---------+---------+-----------------------+
|      Name      |    Owner     | Encoding | Collate |  Ctype  |   Access privileges   |
+----------------+--------------+----------+---------+---------+-----------------------+
| mario_database | freecodecamp | UTF8     | C.UTF-8 | C.UTF-8 |                       |
| postgres       | postgres     | UTF8     | C.UTF-8 | C.UTF-8 |                       |
| template0      | postgres     | UTF8     | C.UTF-8 | C.UTF-8 | =c/postgres          +|
|                |              |          |         |         | postgres=CTc/postgres |
| template1      | postgres     | UTF8     | C.UTF-8 | C.UTF-8 | =c/postgres          +|
|                |              |          |         |         | postgres=CTc/postgres |
+----------------+--------------+----------+---------+---------+-----------------------+
(4 rows)

\d
Did not find any relations.

CREATE TABLE characters();
return  CREATE TABLE if success

ALTER TABLE characters ADD COLUMN character_id SERIAL;
            (tablename)           (column name) (type)
ALTER TABLE table_name ADD COLUMN column_name DATATYPE CONSTRAINT;
                                                        (指定格式)
                                                        比如：NOT NULL

psql --username=freecodecamp --dbname=postgres

CREATE DATABASE database_name;
CREATE TABLE table_name();
ALTER TABLE table_name ADD COLUMN column_name DATATYPE;

ALTER TABLE table_name DROP COLUMN column_name;

DELETE FROM students
WHERE id = 2;

DROP TABLE table_name;

INSERT INTO second_table(id, username) VALUES(1, 'Samus');

INSERT INTO characters(name, homeland, favorite_color)
VALUES('Mario', 'Mushroom Kingdom', 'Red'),
('Luigi', 'Mushroom Kingdom', 'Green'),
('Peach', 'Mushroom Kingdom', 'Pink');

UPDATE students
SET age = 23
WHERE id = 2;

SELECT columns FROM table_name;
选中所有：*

SELECT columns FROM table_name ORDER BY column_name;
SELECT * FROM characters ORDER BY character_id;