PostgreSQL
关系型数据库
官方网站：https://www.postgresql.org/
下载地址：https://www.enterprisedb.com/downloads/postgres-postgresql-downloads
Database
创建数据库
postgres=# \l
数据库列表
名称 | 拥有者 | 字元编码 | 校对规则 | Ctype | 存取权限
-----------+----------+----------+--------------------------------+--------------------------------+-----------------------
postgres | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 |
template0 | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 | =c/postgres +
| | | | | postgres=CTc/postgres
(3 行记录)
postgres=# create database mydb;
CREATE DATABASE
postgres=# \l
数据库列表
名称 | 拥有者 | 字元编码 | 校对规则 | Ctype | 存取权限
-----------+----------+----------+--------------------------------+--------------------------------+-----------------------
mydb | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 |
postgres | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 |
template0 | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 | =c/postgres +
| | | | | postgres=CTc/postgres
(4 行记录)
使用数据库
postgres=# \c mydb;
您现在已经连接到数据库 "mydb",用户 "postgres".
删除数据库
postgres=# drop database mydb
DROP DATABASE
postgres=# \l
数据库列表
名称 | 拥有者 | 字元编码 | 校对规则 | Ctype | 存取权限
-----------+----------+----------+--------------------------------+--------------------------------+-----------------------
postgres | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 |
template0 | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | Chinese (Simplified)_China.936 | Chinese (Simplified)_China.936 | =c/postgres +
| | | | | postgres=CTc/postgres
(3 行记录)
Table
创建表
create table posts (
id serial primary key,
title varchar(255) not null,
content text check(length(content) > 8),
is_draft boolean default true,
is_del boolean default false,
created_date timestamp default 'now'
);
表约束
not null : 不能为空
unique : 在所有数据中的值必须唯一
check : 字段设置条件
default : 默认值
primary key (not null, unique) : 主键
查看表
mydb=# \dt
关联列表
架构模式 | 名称 | 类型 | 拥有者
----------+---------+--------+----------
public | mytable | 数据表 | postgres
public | posts | 数据表 | postgres
mydb=# \d posts;
数据表 "public.posts"
栏位 | 类型 | 校对规则 | 可空的 | 预设
--------------+-----------------------------+----------+----------+-----------------------------------------------------------
id | integer | | not null | nextval('posts_id_seq'::regclass)
title | character varying(255) | | not null |
content | text | | |
is_draft | boolean | | | true
is_del | boolean | | | false
created_date | timestamp without time zone | | | '2020-09-19 11:30:36.484723'::timestamp without time zone
索引：
"posts_pkey" PRIMARY KEY, btree (id)
检查约束限制
"posts_content_check" CHECK (length(content) > 8)
删除表
mydb=# drop table mytable;
DROP TABLE
mydb=# \dt
关联列表
架构模式 | 名称 | 类型 | 拥有者
----------+-------+--------+----------
public | posts | 数据表 | postgres
表结构变更
-
alter table [tablename] …
-
create index …
-
drop index …
mydb=# \d users;
数据表 "public.users"
栏位 | 类型 | 校对规则 | 可空的 | 预设
--------+------------------------+----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
player | character varying(255) | | not null |
score | real | | |
team | character varying(255) | | |
索引：
"users_pkey" PRIMARY KEY, btree (id)
mydb=# alter table users add fullname varchar(255);
ALTER TABLE
mydb=# \d users;
数据表 "public.users"
栏位 | 类型 | 校对规则 | 可空的 | 预设
----------+------------------------+----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
player | character varying(255) | | not null |
score | real | | |
team | character varying(255) | | |
fullname | character varying(255) | | |
索引：
"users_pkey" PRIMARY KEY, btree (id)
mydb=# alter table users drop fullname;
ALTER TABLE
mydb=# \d users;
数据表 "public.users"
栏位 | 类型 | 校对规则 | 可空的 | 预设
--------+------------------------+----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
player | character varying(255) | | not null |
score | real | | |
team | character varying(255) | | |
索引：
"users_pkey" PRIMARY KEY, btree (id)
mydb=# alter table users rename player to nba_player;
ALTER TABLE
mydb=# \d users;
数据表 "public.users"
栏位 | 类型 | 校对规则 | 可空的 | 预设
------------+------------------------+----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
nba_player | character varying(255) | | not null |
score | real | | |
team | character varying(255) | | |
索引：
"users_pkey" PRIMARY KEY, btree (id)
mydb=# alter table users alter nba_player type varchar(100);
ALTER TABLE
mydb=# \d users;
数据表 "public.users"
栏位 | 类型 | 校对规则 | 可空的 | 预设
------------+------------------------+----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
nba_player | character varying(100) | | not null |
score | real | | |
team | character varying(255) | | |
索引：
"users_pkey" PRIMARY KEY, btree (id)
mydb=# create index nba_player_idx on users(nba_player);
CREATE INDEX
mydb=# \d users;
数据表 "public.users"
栏位 | 类型 | 校对规则 | 可空的 | 预设
------------+------------------------+----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
nba_player | character varying(100) | | not null |
score | real | | |
team | character varying(255) | | |
索引：
"users_pkey" PRIMARY KEY, btree (id)
"nba_player_idx" btree (nba_player)
mydb=# drop index nba_player_idx;
DROP INDEX
mydb=# \d users;
数据表 "public.users"
栏位 | 类型 | 校对规则 | 可空的 | 预设
------------+------------------------+----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
nba_player | character varying(100) | | not null |
score | real | | |
team | character varying(255) | | |
索引：
"users_pkey" PRIMARY KEY, btree (id)
索引
缺省时，PostgreSQL 允许在创建索引的同时读取表(SELECT语句)，但是写入表(INSERT, UPDATE, DELETE)的动作将被阻塞到索引创建完毕
索引类型
B-tree
缺省时， CREATE INDEX命令将创建 B-tree 索引，它适合大多数情况。
B-tree 适合处理那些能够按顺序存储的数据之上的等于和范围查询。 特别是在一个建立了索引的字段涉及下面操作符之一进行比较时，PostgreSQL 的查询规划器都会考虑使用 B-tree 索引，索引列中的IS NULL或IS NOT NULL条件可以和B-tree索引一起使用。
<
<=
=
>=
>
between
in
col like 'foo%'
col ~ '^foo
Hash
Hash 索引只能处理简单的等于比较。当一个索引了的列涉及到使用= 操作符进行比较的时候，查询规划器会考虑使用 Hash 索引。下面的命令用于创建 Hash 索引：
CREATE INDEX name ON table USING hash (column);
GiST、SP-GiST、GIN
TODO
字段类型
类型介绍：https://www.postgresql.org/docs/12/datatype.html
数值型
int
real (浮点型)
serial (序列型 - version)
文字型
char (不可变 ， 补空格 TODO)
varchar （可变）
text
布尔型
boolean
日期型
data (年月日)
time (时分秒)
timestamp (年月日时分秒)
特色类型
array
inet (网络地址型)
json
xml
INSERT 语句
- insert into [tablename] (field, …) values (value, …);
当插入SQL由于check函数导致失败时，自增的ID也会被占用。
mydb=# \d users;
Table "public.users"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
name | character varying(20) | | |
age | integer | | |
Indexes:
"users_pkey" PRIMARY KEY, btree (id)
"u_user_age_idx" UNIQUE, btree (name, age)
"u_age_nn_idx" btree (age) WHERE age IS NOT NULL
Number of child tables: 1 (Use \d+ to list them.)
mydb=# SELECT * FROM USERS;
id | name | age
----+-------+-----
2 | Cindy | 16
4 | Dove |
5 | Awa | 14
6 | Seven | 18
1 | Bob | 46
(5 rows)
# 插入相同的 “名称” 和 “年龄” 失败 - 受唯一索引限制
mydb=# insert into users (name, age) values ('Bob', 46);
ERROR: duplicate key value violates unique constraint "u_user_age_idx"
DETAIL: Key (name, age)=(Bob, 46) already exists.
# 插入数据，如果已经存在则忽略
mydb=# insert into users (name, age) values ('Bob', 46) on conflict do nothing;
INSERT 0 0
# 插入数据，如果已经存在则更新 “年龄” 为 47
mydb=# insert into users (name, age) values ('Bob', 46) on conflict (name, age) do update set age = 47;
INSERT 0 1
mydb=# select * from users;
id | name | age
----+-------+-----
2 | Cindy | 16
4 | Dove |
5 | Awa | 14
6 | Seven | 18
1 | Bob | 47
(5 rows)
# 插入数据，如果已经存在则在原来的基础上 加2
mydb=# insert into users (name, age) values ('Bob', 47) on conflict (name, age) do update set age = users.age + 2;
INSERT 0 1
mydb=# select * from users;
id | name | age
----+-------+-----
2 | Cindy | 16
4 | Dove |
5 | Awa | 14
6 | Seven | 18
1 | Bob | 49
(5 rows)
# 插入数据，如果已经存在则在原来的基础上添加上新增的值
mydb=# insert into users (name, age) values ('Bob', 49) on conflict (name, age) do update set age = users.age + excluded.age;
INSERT 0 1
mydb=# select * from users; id | name | age
----+-------+-----
2 | Cindy | 16
4 | Dove |
5 | Awa | 14
6 | Seven | 18
1 | Bob | 98
(5 rows)
SELECT 语句
mydb=# select id, player, score, team from users;
id | player | score | team
----+---------+-------+---------
1 | kuli | 28.3 | yongshi
2 | hadeng | 30.2 | huojian
3 | adu | 25.6 | yongshi
4 | azhan | 27.8 | qishi
5 | shengui | 31.3 | leiting
6 | baibian | 19.8 | rehuo
(6 行记录)
mydb=# select id, player, score, team from users where player like 'a%';
id | player | score | team
----+--------+-------+---------
3 | adu | 25.6 | yongshi
4 | azhan | 27.8 | qishi
(2 行记录)
# _ 为占位符
mydb=# select id, player, score, team from users where player like 'ad_';
id | player | score | team
----+--------+-------+---------
3 | adu | 25.6 | yongshi
(1 行记录)
mydb=# select id, player, score, team from users order by score desc;
id | player | score | team
----+---------+-------+---------
5 | shengui | 31.3 | leiting
2 | hadeng | 30.2 | huojian
1 | kuli | 28.3 | yongshi
4 | azhan | 27.8 | qishi
3 | adu | 25.6 | yongshi
6 | baibian | 19.8 | rehuo
(6 行记录)
# limit {取的条数} offset {偏移量}
mydb=# select id, player, score, team from users order by score desc limit 1 offset 0;
id | player | score | team
----+---------+-------+---------
5 | shengui | 31.3 | leiting
(1 行记录)
mydb=# select id, player, score, team from users order by score desc limit 1 offset 1;
id | player | score | team
----+--------+-------+---------
2 | hadeng | 30.2 | huojian
(1 行记录)
mydb=# select id, player, score, team from users order by score desc limit 2 offset 1;
id | player | score | team
----+--------+-------+---------
2 | hadeng | 30.2 | huojian
1 | kuli | 28.3 | yongshi
(2 行记录)
mydb=# select id, player, score, team from users order by score desc limit 2 offset 2;
id | player | score | team
----+--------+-------+---------
1 | kuli | 28.3 | yongshi
4 | azhan | 27.8 | qishi
(2 行记录)
mydb=# select team, max(score) from users group by team;
team | max
---------+------
yongshi | 28.3
qishi | 27.8
rehuo | 19.8
leiting | 31.3
huojian | 30.2
(5 行记录)
mydb=# select team, max(score) from users group by team having max(score) > 30;
team | max
---------+------
leiting | 31.3
huojian | 30.2
(2 行记录)
mydb=# select team, max(score) from users group by team having max(score) > 30 order by max(score);
team | max
---------+------
huojian | 30.2
leiting | 31.3
(2 行记录)
mydb=# select id, player, score, team, concat(player, '/', team) as "info" from users;
id | player | score | team | info
----+---------+-------+---------+-----------------
1 | kuli | 28.3 | yongshi | kuli/yongshi
2 | hadeng | 30.2 | huojian | hadeng/huojian
3 | adu | 25.6 | yongshi | adu/yongshi
4 | azhan | 27.8 | qishi | azhan/qishi
5 | shengui | 31.3 | leiting | shengui/leiting
6 | baibian | 19.8 | rehuo | baibian/rehuo
(6 行记录)
# 对数据进行随机排序 (random() 获取随机数)
mydb=# select id, player, score, team from users order by random();
id | player | score | team
----+---------+-------+---------
2 | hadeng | 30.2 | huojian
3 | adu | 25.6 | yongshi
6 | baibian | 19.8 | rehuo
5 | shengui | 31.3 | leiting
4 | azhan | 27.8 | qishi
1 | kuli | 28.3 | yongshi
(6 行记录)
# select for update
# [线程A] 开启事务
mydb=# begin;
BEGIN
# [线程A] 查询 ID = 1 的数据，并加锁
mydb=# select * from users where id = 1 for update;
id | name | age
----+------+-----
1 | Bob | 21
(1 row)
# [线程B] 更新阻塞
mydb=# update users set age = 22 where id = 1;
# [线程A] 提交事务
mydb=# commit;
# [线程B] 更新成功
UPDATE 1
表关联
mydb=# select * from twitters;
id | user_id | content
----+---------+----------------------------------
1 | 1 | 今天又是大胜,克莱打的真好!
2 | 2 | 今晚我得了60分,哈哈!
3 | 3 | 获胜咱不怕,缺谁谁尴尬.
4 | 4 | 明年我也可能转会西部
5 | 5 | 我都双20+了，怎么球队就是不胜呢?
6 | 1 | 明年听说有条大鱼要来,谁呀?
(6 行记录)
mydb=# select * from users;
id | nba_player | score | team
----+------------+-------+---------
1 | kuli | 28.3 | yongshi
2 | hadeng | 30.2 | huojian
3 | adu | 25.6 | yongshi
5 | shengui | 31.3 | leiting
6 | baibian | 19.8 | rehuo
4 | azhan | 29.1 | qishi
(6 行记录)
mydb=# select * from users u, twitters t where u.id = t.user_id;
id | nba_player | score | team | id | user_id | content
----+------------+-------+---------+----+---------+----------------------------------
1 | kuli | 28.3 | yongshi | 1 | 1 | 今天又是大胜,克莱打的真好!
2 | hadeng | 30.2 | huojian | 2 | 2 | 今晚我得了60分,哈哈!
3 | adu | 25.6 | yongshi | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
4 | azhan | 29.1 | qishi | 4 | 4 | 明年我也可能转会西部
5 | shengui | 31.3 | leiting | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
1 | kuli | 28.3 | yongshi | 6 | 1 | 明年听说有条大鱼要来,谁呀?
(6 行记录)
mydb=# select * from users u join twitters t on u.id = t.user_id;
id | nba_player | score | team | id | user_id | content
----+------------+-------+---------+----+---------+----------------------------------
1 | kuli | 28.3 | yongshi | 1 | 1 | 今天又是大胜,克莱打的真好!
2 | hadeng | 30.2 | huojian | 2 | 2 | 今晚我得了60分,哈哈!
3 | adu | 25.6 | yongshi | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
4 | azhan | 29.1 | qishi | 4 | 4 | 明年我也可能转会西部
5 | shengui | 31.3 | leiting | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
1 | kuli | 28.3 | yongshi | 6 | 1 | 明年听说有条大鱼要来,谁呀?
(6 行记录)
# left join 等同与 left outer join
mydb=# select * from users u left join twitters t on u.id = t.user_id;
id | nba_player | score | team | id | user_id | content
----+------------+-------+---------+----+---------+----------------------------------
1 | kuli | 28.3 | yongshi | 1 | 1 | 今天又是大胜,克莱打的真好!
2 | hadeng | 30.2 | huojian | 2 | 2 | 今晚我得了60分,哈哈!
3 | adu | 25.6 | yongshi | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
4 | azhan | 29.1 | qishi | 4 | 4 | 明年我也可能转会西部
5 | shengui | 31.3 | leiting | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
1 | kuli | 28.3 | yongshi | 6 | 1 | 明年听说有条大鱼要来,谁呀?
6 | baibian | 19.8 | rehuo | | |
(7 行记录)
mydb=# select * from users u left outer join twitters t on u.id = t.user_id;
id | nba_player | score | team | id | user_id | content
----+------------+-------+---------+----+---------+----------------------------------
1 | kuli | 28.3 | yongshi | 1 | 1 | 今天又是大胜,克莱打的真好!
2 | hadeng | 30.2 | huojian | 2 | 2 | 今晚我得了60分,哈哈!
3 | adu | 25.6 | yongshi | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
4 | azhan | 29.1 | qishi | 4 | 4 | 明年我也可能转会西部
5 | shengui | 31.3 | leiting | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
1 | kuli | 28.3 | yongshi | 6 | 1 | 明年听说有条大鱼要来,谁呀?
6 | baibian | 19.8 | rehuo | | |
(7 行记录)
# cross join 为全部交叉关联 (此时数据量很大，慎用)
mydb=# select * from users u cross join twitters t;
id | nba_player | score | team | id | user_id | content
----+------------+-------+---------+----+---------+----------------------------------
1 | kuli | 28.3 | yongshi | 1 | 1 | 今天又是大胜,克莱打的真好!
2 | hadeng | 30.2 | huojian | 1 | 1 | 今天又是大胜,克莱打的真好!
3 | adu | 25.6 | yongshi | 1 | 1 | 今天又是大胜,克莱打的真好!
5 | shengui | 31.3 | leiting | 1 | 1 | 今天又是大胜,克莱打的真好!
6 | baibian | 19.8 | rehuo | 1 | 1 | 今天又是大胜,克莱打的真好!
4 | azhan | 29.1 | qishi | 1 | 1 | 今天又是大胜,克莱打的真好!
1 | kuli | 28.3 | yongshi | 2 | 2 | 今晚我得了60分,哈哈!
2 | hadeng | 30.2 | huojian | 2 | 2 | 今晚我得了60分,哈哈!
3 | adu | 25.6 | yongshi | 2 | 2 | 今晚我得了60分,哈哈!
5 | shengui | 31.3 | leiting | 2 | 2 | 今晚我得了60分,哈哈!
6 | baibian | 19.8 | rehuo | 2 | 2 | 今晚我得了60分,哈哈!
4 | azhan | 29.1 | qishi | 2 | 2 | 今晚我得了60分,哈哈!
1 | kuli | 28.3 | yongshi | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
2 | hadeng | 30.2 | huojian | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
3 | adu | 25.6 | yongshi | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
5 | shengui | 31.3 | leiting | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
6 | baibian | 19.8 | rehuo | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
4 | azhan | 29.1 | qishi | 3 | 3 | 获胜咱不怕,缺谁谁尴尬.
1 | kuli | 28.3 | yongshi | 4 | 4 | 明年我也可能转会西部
2 | hadeng | 30.2 | huojian | 4 | 4 | 明年我也可能转会西部
3 | adu | 25.6 | yongshi | 4 | 4 | 明年我也可能转会西部
5 | shengui | 31.3 | leiting | 4 | 4 | 明年我也可能转会西部
6 | baibian | 19.8 | rehuo | 4 | 4 | 明年我也可能转会西部
4 | azhan | 29.1 | qishi | 4 | 4 | 明年我也可能转会西部
1 | kuli | 28.3 | yongshi | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
2 | hadeng | 30.2 | huojian | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
3 | adu | 25.6 | yongshi | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
5 | shengui | 31.3 | leiting | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
6 | baibian | 19.8 | rehuo | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
4 | azhan | 29.1 | qishi | 5 | 5 | 我都双20+了，怎么球队就是不胜呢?
1 | kuli | 28.3 | yongshi | 6 | 1 | 明年听说有条大鱼要来,谁呀?
2 | hadeng | 30.2 | huojian | 6 | 1 | 明年听说有条大鱼要来,谁呀?
3 | adu | 25.6 | yongshi | 6 | 1 | 明年听说有条大鱼要来,谁呀?
5 | shengui | 31.3 | leiting | 6 | 1 | 明年听说有条大鱼要来,谁呀?
更新与删除
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update [tablename] set [field=newvalue, …] where …
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delete from [tablename] where …
视图
视图概念
视图（View）是从一个或多个表导出的对象。视图与表不同，视图是一个虚表，即视图所对应的数据不进行实际存储，数据库中只存储视图的定义，在对视图的数据进行操作时，系统根据视图的定义去操作与视图相关联的基本表。
简单理解
视图就是一个SELECT语句，把业务系统中常用的SELECT语句简化成一个类似于表的对象，便于简单读取和开发。
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create view …
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drop view …
# 创建视图
mydb=# create view curry_twitters as select u.nba_player, t.content from users as u, twitters as t where u.id = t.user_id and u.id = 1;
CREATE VIEW
# 查询所有视图
mydb=# \dv
关联列表
架构模式 | 名称 | 类型 | 拥有者
----------+----------------+------+----------
public | curry_twitters | 视图 | postgres
(1 行记录)
# 查看指定视图的定义
mydb=# \d curry_twitters;
视图 "public.curry_twitters"
栏位 | 类型 | 校对规则 | 可空的 | 预设
------------+------------------------+----------+--------+------
nba_player | character varying(100) | | |
content | character varying(255) | | |
mydb=# select * from curry_twitters;
nba_player | content
------------+----------------------------
kuli | 今天又是大胜,克莱打的真好!
kuli | 明年听说有条大鱼要来,谁呀?
(2 行记录)
mydb=# select * from twitters;
id | user_id | content
----+---------+----------------------------------
1 | 1 | 今天又是大胜,克莱打的真好!
2 | 2 | 今晚我得了60分,哈哈!
3 | 3 | 获胜咱不怕,缺谁谁尴尬.
4 | 4 | 明年我也可能转会西部
5 | 5 | 我都双20+了，怎么球队就是不胜呢?
6 | 1 | 明年听说有条大鱼要来,谁呀?
(6 行记录)
mydb=# update twitters set content = '变更后的值' where id = 1;
UPDATE 1
mydb=# select * from curry_twitters;
nba_player | content
------------+----------------------------
kuli | 明年听说有条大鱼要来,谁呀?
kuli | 变更后的值
(2 行记录)
# 删除视图
mydb=# drop view curry_twitters;
DROP VIEW
mydb=# \dv
没有找到任何关系.
事务
数据库事务(Database Transaction) ，是指作为单个逻辑工作单元执行的一系列操作，要么完全地执行，要么完全地不执行。 事务处理可以确保除非事务性单元内的所有操作都成功完成，否则不会永久更新面向数据的资源。通过将一组相关操作组合为一个要么全部成功要么全部失败的单元，可以简化错误恢复并使应用程序更加可靠。一个逻辑工作单元要成为事务，必须满足所谓的ACID（原子性、一致性、隔离性和持久性）属性。事务是数据库运行中的逻辑工作单位，由DBMS中的事务管理子系统负责事务的处理。
-
begin
-
commit
-
rollback
mydb=# select * from users;
id | nba_player | score | team
----+------------+-------+---------
1 | kuli | 28.3 | yongshi
2 | hadeng | 30.2 | huojian
3 | adu | 25.6 | yongshi
5 | shengui | 31.3 | leiting
6 | baibian | 19.8 | rehuo
4 | azhan | 29.1 | qishi
(6 行记录)
# 开启事务
mydb=# begin;
BEGIN
mydb=# update users set score = 50.0 where id = 1;
UPDATE 1
mydb=# update users set score = 60 where id = 2;
UPDATE 1
# 事务提交前查询 (可以查询到未提交读 - 与事务隔离级别有关)
mydb=# select * from users;
id | nba_player | score | team
----+------------+-------+---------
3 | adu | 25.6 | yongshi
5 | shengui | 31.3 | leiting
6 | baibian | 19.8 | rehuo
4 | azhan | 29.1 | qishi
1 | kuli | 50 | yongshi
2 | hadeng | 60 | huojian
(6 行记录)
# 事务回滚
mydb=# rollback;
ROLLBACK
# 再次查询，数据为原始数据
mydb=# select * from users;
id | nba_player | score | team
----+------------+-------+---------
1 | kuli | 28.3 | yongshi
2 | hadeng | 30.2 | huojian
3 | adu | 25.6 | yongshi
5 | shengui | 31.3 | leiting
6 | baibian | 19.8 | rehuo
4 | azhan | 29.1 | qishi
(6 行记录)
# 开始事务
mydb=# begin;
BEGIN
mydb=# update users set score = 50.0 where id = 1;
UPDATE 1
mydb=# update users set score = 60 where id = 2;
UPDATE 1
# 提价事务
mydb=# commit;
COMMIT
mydb=# select * from users;
id | nba_player | score | team
----+------------+-------+---------
3 | adu | 25.6 | yongshi
5 | shengui | 31.3 | leiting
6 | baibian | 19.8 | rehuo
4 | azhan | 29.1 | qishi
1 | kuli | 50 | yongshi
2 | hadeng | 60 | huojian
(6 行记录)