PostgreSQL 基础知识

执行环境： psql

1. 创建一个表格

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	
);
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• 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

INSERT INTO customers(firstname, lastname, username, password, email, created_on)
VALUES('Elizabeth', 'Banks', 'elizabethbanks', '4s$5eks9m', 'elizabethbanks@myemail.com', CURRENT_TIMESTAMP);
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SELECT * FROM customers;
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插入两条记录

INSERT INTO customers(firstname, lastname, username, password, email, created_on)
VALUES('Nicole', 'Kidman', 'nkidman', '392kMLK!m', 'nicole@kidman.com', CURRENT_TIMESTAMP),
('Leroy', 'Jenkins', 'leeroy', '4k2ln@Lm', 'leroy@email.com', CURRENT_TIMESTAMP);
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SELECT * FROM customers;
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3. 修改

UPDATE customers
SET username='aliceinwonderland'
WHERE email=
'elizabethbanks@myemail.com';
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SELECT * FROM customers;
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4. 查找

SELECT * FROM customers WHERE username='aliceinwonderland';
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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。

SELECT username FROM customers WHERE email LIKE '%@myemail.com';
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利用选择的数据创建一个新表

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

选择的数据将按照"lastname"字段进行降序排列

SELECT firstname, lastname
FROM customers
ORDER BY lastname DESC;
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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。

SELECT firstname || ' ' || lastname fullname, email, LENGTH(password) passwordlength
FROM customers
ORDER BY passwordlength;
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选择 password 长度小于9的数据

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

使用RETURNING关键字，返回受影响的行。

DELETE FROM customers
WHERE customer_id = 1
RETURNING *;
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从"customers"表中删除"username"字段不等于’nkidman’的行

DELETE FROM customers
WHERE username <> 'nkidman'
RETURNING *;
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从"customers"表中删除所有行。

DELETE FROM customers
RETURNING *;
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7. 创建只读用户

该用户的有效期截止到’2024-02-02’。

CREATE USER readitralph
WITH PASSWORD 'password'
VALID UNTIL '2024-02-02';
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授予名为"readitralph"的用户对数据库中所有数据的读取权限。

GRANT pg_read_all_data TO readitralph;
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