PostgreSQL 基础知识

执行环境： psql

1. 创建一个表格

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CREATE TABLE customers (
customer_id serial PRIMARY KEY,
	firstname VARCHAR(100) NOT NULL,
	lastname VARCHAR(100) NOT NULL,
	username VARCHAR(50) UNIQUE NOT NULL,
	password VARCHAR(50) NOT NULL,
	email VARCHAR(255) UNIQUE NOT NULL,
	created_on TIMESTAMPTZ NOT NULL	
);

customer_id：这是一个序列，意味着它将自动递增，用作主键，用来唯一标识每个客户。
created_on：这是一个不允许为空的日期时间字段，用来存储客户的创建时间。

2. 插入

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INSERT INTO customers(firstname, lastname, username, password, email, created_on)
VALUES('Elizabeth', 'Banks', 'elizabethbanks', '4s$5eks9m', '[email protected]', CURRENT_TIMESTAMP);

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SELECT * FROM customers;

插入两条记录

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INSERT INTO customers(firstname, lastname, username, password, email, created_on)
VALUES('Nicole', 'Kidman', 'nkidman', '392kMLK!m', '[email protected]', CURRENT_TIMESTAMP),
('Leroy', 'Jenkins', 'leeroy', '4k2ln@Lm', '[email protected]', CURRENT_TIMESTAMP);

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SELECT * FROM customers;

3. 修改

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UPDATE customers
SET username='aliceinwonderland'
WHERE email=
'[email protected]';

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SELECT * FROM customers;

4. 查找

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SELECT * FROM customers WHERE username='aliceinwonderland';

仅当"email"字段的值满足特定模式时才被选择，这个模式是以"@myemail.com"结尾的，而"%"符号表示可以有零个或多个字符。

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SELECT username FROM customers WHERE email LIKE '%@myemail.com';

利用选择的数据创建一个新表

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CREATE TABLE usernames AS SELECT username FROM customers WHERE email LIKE '%@myemail.com';

5. 排序

选择的数据将按照"lastname"字段进行降序排列

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SELECT firstname, lastname
FROM customers
ORDER BY lastname DESC;

返回的结果将会包含每个客户的完整姓名、邮箱地址以及密码的长度，并且按照密码长度从短到长进行排序。

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SELECT firstname || ' ' || lastname fullname, email, LENGTH(password) passwordlength
FROM customers
ORDER BY passwordlength;

选择 password 长度小于9的数据

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SELECT firstname || ' ' || lastname fullname, email, LENGTH(password) passwordlength
FROM customers
WHERE LENGTH(password) < 9
ORDER BY passwordlength;

6. 删除

使用RETURNING关键字，返回受影响的行。

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DELETE FROM customers
WHERE customer_id = 1
RETURNING *;

从"customers"表中删除"username"字段不等于'nkidman'的行

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DELETE FROM customers
WHERE username <> 'nkidman'
RETURNING *;

从"customers"表中删除所有行。

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DELETE FROM customers
RETURNING *;

7. 创建只读用户

该用户的有效期截止到'2024-02-02'。

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CREATE USER readitralph
WITH PASSWORD 'password'
VALID UNTIL '2024-02-02';

授予名为"readitralph"的用户对数据库中所有数据的读取权限。

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GRANT pg_read_all_data TO readitralph;