一. PostgreSQL 简介
1 资料来源：
中文手册：http://www.postgres.cn/docs/14/index.html
知乎链接：https://www.zhihu.com/column/c_1452567507496689664
视频链接：https://www.bilibili.com/video/BV1uW4y1m7pD/?spm_id_from=pageDriver&vd_source=372365c1ea72bb6075a0ec1b05671b3a
二. PostgreSQL 安装
1 docker 安装
拉取镜像
docker pull postgres
创建容器
docker run -itd --name postgres -e POSTGRES_PASSWORD=root -p 5432:5432 postgres:15
三. SQL语言
1. DDL
2. DML
CREATE TABLE products (
product_no integer,
name text,
price numeric
);
2.1 insert
- 单行
INSERT INTO products VALUES (1, 'Cheese', 9.99);
INSERT INTO products (product_no, name, price) VALUES (1, 'Cheese', 9.99);
INSERT INTO products (product_no, name) VALUES (1, 'Cheese');
INSERT INTO products VALUES (1, 'Cheese');
- 多行
INSERT INTO products (product_no, name, price) VALUES
(1, 'Cheese', 9.99),
(2, 'Bread', 1.99),
(3, 'Milk', 2.99);
INSERT INTO products (product_no, name, price)
SELECT product_no, name, price FROM new_products
WHERE release_date = 'today';
2.2 update
UPDATE products SET price = 10 WHERE price = 5;
UPDATE mytable SET a = 5, b = 3, c = 1 WHERE a > 0;
2.3 delete
DELETE FROM products WHERE price = 10;
DELETE FROM products;
2.4 数据合并
insert into public.user(id,username,password) values(15,'root','root')
on conflict (id)
do update set username = excluded.username, password = excluded.password
2.5 CTE和通用表表达式
- 插入
with inserts as
(
insert into employees values(1234,'1','1','1','1','2008-03-08','ST_CLERK',1.00,0.1,'120','90')
returning *
)
insert into employees_his select * from inserts;
- 更新
with updates as
(
update employees
set salary = salary + 500
where salary = 2100
returning *
)
select * into employees_his from updates
with updates as
(
update employees
set salary = salary + 500
where salary = 2100
returning *
)
insert into employees_his select * from updates;
3. DQL
3.1 通用表表达式
with tempA as (
select * from public.goods where id < 4
),
tempB as (
select * from public.goods where id >= 4
)
select * from tempA
union all
select * from tempB
3.2 递归查询语句
with recursive cte(n) as
(
select 1
union ALL
select n + 1 from cte where n < 5
)
select * from cte
3.3 窗口函数
3.3.1 定义
窗口函数，也叫OLAP(Online Anallytical Processing,联机分析处理）,可以对数据库数据进行实时分析处理
3.3.2 常用的窗口函数
sum
avg
max
min
count
rank
row_number
3.3.3 格式
window_function ( expr ) over (
partition by …
order by …
frame_clause
)
window_function是窗口名称，expr是函数参数，有些函数不需要参数，
over子句包含：三部分
- 分区：partition by
- 排序：order by
- 窗口大小：frame_clause
3.3.4 示例
select department_id, hire_date, salary, sum(salary) over (partition by department_id order by salary)
from public.employees;
select department_id, hire_date, salary, rank() over (partition by department_id order by salary desc)
from public.employees;
select department_id, hire_date, salary, row_number() over (partition by department_id order by salary desc)
from public.employees;
4. 数据类型
四. 高级特性
1. 事务与并发控制
1.1 acid特性
原子性
一致性
隔离性
持久性
1.2 事务控制语句
begin;
insert into employees values(1234,'1','1','1','1','2008-03-08','ST_CLERK',1.00,0.1,'120','90');
insert into employees values(1235,'1','1','1','1','2008-03-08','ST_CLERK',1.00,0.1,'120','90');
commit; // rollback
1.3 并发和隔离
脏读：一个事务可以读取到其他事务未提交的修改；
不可重复读：一个事务读取某个记录后，再次读取该记录时数据发生了改变（被其他事务修改并提交）；
幻读：一个事务按照某个条件查询一些数据后，再次执行相同查询时结果的数量发生的改变（另一个事务增加或删除了某些数据并完成提交）；
更新丢失：两个事务同时读取某一条记录，分别进行修改提交，就会造成先修改的事务的修改丢失。
