PostgreSQL 学习笔记
之前的话，MySQL 接触得稍微多一些，最近由于工作的原因，刚好以一个菜鸟的身份来学学 PostgreSQL。
常用快捷命令
其实用 \? 就可以把所有快捷命令及其解释就都显示出来了。
\? 显示所有快捷命令及其注解
\l 显示可用的数据库
\c 进入具体的数据库
\d 显示可用的数据表
\d 查看表信息
\di 查看数据库所有索引
\dv 查看数据库所有视图
\du 查看数据库所有角色
\h 显示指定命令帮助信息
\q 退出 psql 命令行
\x 行/列 模式切换（类似于 sqlite 中的 .mode line 和 .mode column）
... psql 命令参数
root@localhost ~# psql --help
psql is the PostgreSQL interactive terminal.
Usage:
psql [OPTION]... [DBNAME [USERNAME]]
General options:
-c, --command=COMMAND run only single command (SQL or internal) and exit
-d, --dbname=DBNAME database name to connect to (default: "root")
-f, --file=FILENAME execute commands from file, then exit
-l, --list list available databases, then exit
-v, --set=, --variable=NAME=VALUE
set psql variable NAME to VALUE
(e.g., -v ON_ERROR_STOP=1)
-V, --version output version information, then exit
-X, --no-psqlrc do not read startup file (~/.psqlrc)
-1 ("one"), --single-transaction
execute as a single transaction (if non-interactive)
-?, --help[=options] show this help, then exit
--help=commands list backslash commands, then exit
--help=variables list special variables, then exit
Input and output options:
-a, --echo-all echo all input from script
-b, --echo-errors echo failed commands
-e, --echo-queries echo commands sent to server
-E, --echo-hidden display queries that internal commands generate
-L, --log-file=FILENAME send session log to file
-n, --no-readline disable enhanced command line editing (readline)
-o, --output=FILENAME send query results to file (or |pipe)
-q, --quiet run quietly (no messages, only query output)
-s, --single-step single-step mode (confirm each query)
-S, --single-line single-line mode (end of line terminates SQL command)
Output format options:
-A, --no-align unaligned table output mode
--csv CSV (Comma-Separated Values) table output mode
-F, --field-separator=STRING
field separator for unaligned output (default: "|")
-H, --html HTML table output mode
-P, --pset=VAR[=ARG] set printing option VAR to ARG (see \pset command)
-R, --record-separator=STRING
record separator for unaligned output (default: newline)
-t, --tuples-only print rows only
-T, --table-attr=TEXT set HTML table tag attributes (e.g., width, border)
-x, --expanded turn on expanded table output
-z, --field-separator-zero
set field separator for unaligned output to zero byte
-0, --record-separator-zero
set record separator for unaligned output to zero byte
Connection options:
-h, --host=HOSTNAME database server host or socket directory (default: "local socket")
-p, --port=PORT database server port (default: "5432")
-U, --username=USERNAME database user name (default: "root")
-w, --no-password never prompt for password
-W, --password force password prompt (should happen automatically)
psql -d public -U postgres -p 5450 -c "delete from license"安装
我自己是 centos7.6 虚拟机，通过选择系统和版本，官方就会提供了一个 yum 安装的命令：
sudo yum install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
sudo yum install -y postgresql13-server
sudo /usr/pgsql-13/bin/postgresql-13-setup initdb
sudo systemctl enable postgresql-13
sudo systemctl start postgresql-13
执行一下就差不多了，安装完毕后，系统会创建一个数据库超级用户 postgres，密码为空。
root@master ~# psql --version
psql (PostgreSQL) 9.2.24
root@master ~# cat /etc/passwd | grep postgres
postgres:x:26:26:PostgreSQL Server:/var/lib/pgsql:/bin/bash
这时使用以下命令进入 postgres 命令行了。
root@master ~# sudo -i -u postgres
-bash-4.2$ pwd
/var/lib/pgsql
-bash-4.2$ psql
psql (9.2.24, server 13.7)
WARNING: psql version 9.2, server version 13.0.
Some psql features might not work.
Type "help" for help.
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
(3 rows)
修改密码
修改数据库用户 postgres 的密码
postgres=# ALTER USER postgres WITH PASSWORD 'postgres';
配置允许远程连接
进入安装目录
如果是默认安装的话，路径和下面的应该差不多，后边按照实际版本指定一下路径就好了。
root@master ~# cd /var/lib/pgsql/13/data
root@master /v/l/p/1/data# pwd
/var/lib/pgsql/13/data
编辑 pg_hba.conf
添加一行
编辑 postgresql.conf
防火墙开放 5432 端口
firewall-cmd --zone=public --add-port=5432/tcp --permanent
firewall-cmd --reload重启 pgsql 数据库服务
systemctl restart postgresql-13.serviceNavicat 连接测试
数据库创建（create database ;）
在 postgres 命令行的话，就用 create database
postgres=# CREATE DATABASE looking;
CREATE DATABASE
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
looking | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
(4 rows)
在 linux 命令行的话，可以使用 createdb 命令创建数据库。
-bash-4.2$ createdb world
-bash-4.2$ psql
psql (9.2.24, server 13.7)
WARNING: psql version 9.2, server version 13.0.
Some psql features might not work.
Type "help" for help.
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
hello | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
looking | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
world | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
(6 rows)
postgres 的默认端口是 5432。
-bash-4.2$ cat /etc/services | grep 5432
postgres 5432/tcp postgresql # POSTGRES
postgres 5432/udp postgresql # POSTGRES
创建数据库的时候可以使用 -p 命令指定其他端口。
createdb -h localhost -p 5435 -U postgres looking选择数据库（\c ）
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
hello | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
looking | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
world | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
(6 rows)
postgres=# \c looking
psql (9.2.24, server 13.7)
WARNING: psql version 9.2, server version 13.0.
Some psql features might not work.
You are now connected to database "looking" as user "postgres".
删除数据库（drop database ;）
DROP DATABASE [ IF EXISTS ] name
postgres=# drop database world;
DROP DATABASE
和创建数据库一样，也可以在 linux 命令行使用 dropdb 删除数据库。
-bash-4.2$ dropdb hello
-bash-4.2$ psql
psql (9.2.24, server 13.7)
WARNING: psql version 9.2, server version 13.0.
Some psql features might not work.
Type "help" for help.
postgres=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
looking | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
postgres | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 |
template0 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
template1 | postgres | UTF8 | en_US.UTF-8 | en_US.UTF-8 | =c/postgres +
| | | | | postgres=CTc/postgres
(4 rows)
创建表（create table ;）
数据表的创建和 mysql 的语法差不多，创建完以后可以用 \d 查看已创建的数据表信息。
looking=# drop table company;
DROP TABLE
looking=# \d
No relations found.
looking=# CREATE TABLE COMPANY(
looking(# ID INT PRIMARY KEY NOT NULL,
looking(# NAME TEXT NOT NULL,
looking(# AGE INT NOT NULL,
looking(# ADDRESS CHAR(50),
looking(# SALARY REAL
looking(# );
CREATE TABLE
looking=# CREATE TABLE DEPARTMENT(
looking(# ID INT PRIMARY KEY NOT NULL,
looking(# DEPT CHAR(50) NOT NULL,
looking(# EMP_ID INT NOT NULL
looking(# );
CREATE TABLE
looking=# \d
List of relations
Schema | Name | Type | Owner
--------+------------+-------+----------
public | company | table | postgres
public | department | table | postgres
(2 rows)
删除表（drop table ;）
PostgreSQL 使用 DROP TABLE 语句来删除表格，包含表格数据、规则、触发器等。
looking=# \d
List of relations
Schema | Name | Type | Owner
--------+------------+-------+----------
public | company | table | postgres
public | department | table | postgres
(2 rows)
looking=# drop table company, department;
DROP TABLE
looking=# \d
No relations found.
模式
PostgreSQL 模式（SCHEMA）可以看着是一个表的集合。一个模式可以包含视图、索引、数据类型、函数和操作符等。相同的对象名称可以被用于不同的模式中而不会出现冲突，类似数据库里边的命名空间。
looking=# create schema myschema;
CREATE SCHEMA
looking=# drop schema myschema;
DROP SCHEMA
插入数据
looking=# CREATE TABLE COMPANY(
looking(# ID INT PRIMARY KEY NOT NULL,
looking(# NAME TEXT NOT NULL,
looking(# AGE INT NOT NULL,
looking(# ADDRESS CHAR(50),
looking(# SALARY REAL,
looking(# JOIN_DATE DATE
looking(# );
CREATE TABLE
looking=# \d
List of relations
Schema | Name | Type | Owner
--------+---------+-------+----------
public | company | table | postgres
(1 row)
looking=# INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY,JOIN_DATE) VALUES (1, 'Paul', 32, 'California', 20000.00,'2001-07-13');
INSERT 0 1
looking=# INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,JOIN_DATE) VALUES (2, 'Allen', 25, 'Texas', '2007-12-13');
INSERT 0 1
looking=# INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY,JOIN_DATE) VALUES (3, 'Teddy', 23, 'Norway', 20000.00, DEFAULT );
INSERT 0 1
looking=# INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY,JOIN_DATE) VALUES
(4, 'Mark', 25, 'Rich-Mond ', 65000.00, '2007-12-13' ),
(5, 'David', 27, 'Texas', 85000.00, '2007-12-13');
INSERT 0 2
查询数据
looking=# select * from company;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
2 | Allen | 25 | Texas | | 2007-12-13
3 | Teddy | 23 | Norway | 20000 |
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
(5 rows)
运算符
PostgreSQL 运算符是一个保留关键字或字符，一般用在 WHERE 语句中，作为过滤条件。假设变量 a 为 2，变量 b 为 3，则：
| 运算符 | 描述 | 实例 |
|---|---|---|
| + | 加 | a + b 结果为 5 |
| - | 减 | a - b 结果为 -1 |
| * | 乘 | a * b 结果为 6 |
| / | 除 | b / a 结果为 1 |
| % | 模（取余） | b % a 结果为 1 |
| ^ | 指数 | a ^ b 结果为 8 |
| |/ | 平方根 | |/ 25.0 结果为 5 |
| ||/ | 立方根 | ||/ 27.0 结果为 3 |
| ! | 阶乘 | 5 ! 结果为 120 |
| !! | 阶乘（前缀操作符） | !! 5 结果为 120 |
looking=# select 5!;
?column?
----------
120
(1 row)
表达式
布尔表达式
looking=# SELECT * FROM COMPANY WHERE SALARY = 20000;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
3 | Teddy | 23 | Norway | 20000 |
(2 rows)
数字表达式
looking=# SELECT (17 + 6) AS ADDITION ;
addition
----------
23
(1 row)
looking=# SELECT COUNT(*) AS "RECORDS" FROM COMPANY;
RECORDS
---------
5
(1 row)
日期表达式
looking=# SELECT CURRENT_TIMESTAMP;
current_timestamp
-------------------------------
2022-06-07 18:19:20.020001+08
(1 row)
常规操作
我自己大概看了一下，这些常规操作和 MySQL 好像没太大区别，至少从表象上来看是这样的，所以就不多赘述了，简单列几个例子看看就好。
WHERE
可以在 WHERE 子句中使用比较运算符或逻辑运算符，例如 >, <, =, LIKE, NOT 等等。
looking=# SELECT * FROM COMPANY WHERE SALARY > 30000;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
(2 rows)
AND / OR
looking=# SELECT * FROM COMPANY WHERE AGE >=25 AND SALARY > 65000;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
5 | David | 27 | Texas | 85000 | 2007-12-13
(1 row)
looking=# SELECT * FROM COMPANY WHERE AGE >=25 OR SALARY > 65000;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
2 | Allen | 25 | Texas | | 2007-12-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
(4 rows)
UPDATE
looking=# SELECT * FROM COMPANY;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
2 | Allen | 25 | Texas | | 2007-12-13
3 | Teddy | 23 | Norway | 20000 |
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
(5 rows)
looking=# UPDATE COMPANY SET SALARY = 15000 WHERE ID=3;
UPDATE 1
looking=# SELECT * FROM COMPANY;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
2 | Allen | 25 | Texas | | 2007-12-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
3 | Teddy | 23 | Norway | 15000 |
(5 rows)
DELETE
looking=# SELECT * FROM COMPANY;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
2 | Allen | 25 | Texas | | 2007-12-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
3 | Teddy | 23 | Norway | 15000 |
(5 rows)
looking=# DELETE FROM COMPANY WHERE ID=2;
DELETE 1
looking=# SELECT * FROM COMPANY;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
3 | Teddy | 23 | NoLIKE
在 PostgreSQL 中，主要有以下两种通配符：百分号 % （%通配任意个任意字符）和 下划线 _（_通配一个任意字符）。对于非文本类型的字段，记得通配字段后边要加上 ::text 将相应字段类型转换为字符串数据类型再进行匹配。
looking=# SELECT * FROM COMPANY WHERE AGE LIKE '3%';
ERROR: operator does not exist: integer ~~ unknown
LINE 1: SELECT * FROM COMPANY WHERE AGE LIKE '3%';
^
HINT: No operator matches the given name and argument types. You might need to add explicit type casts.
looking=# SELECT * FROM COMPANY WHERE AGE::text LIKE '3%';
id | name | age | address | salary | join_date
----+------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
(1 row)
looking=# SELECT * FROM COMPANY WHERE ADDRESS::text LIKE '_o%';
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+-----------
3 | Teddy | 23 | Norway | 15000 |
(1 row)
looking=# SELECT * FROM COMPANY WHERE ADDRESS::text LIKE '%o%';
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
3 | Teddy | 23 | Norway | 15000 |
(3 rows)
LIMIT
looking=# SELECT * FROM COMPANY;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
3 | Teddy | 23 | Norway | 15000 |
(4 rows)
looking=# SELECT * FROM COMPANY LIMIT 2;
id | name | age | address | salary | join_date
----+------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
(2 rows)
ORDER BY
looking=# SELECT * FROM COMPANY;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
3 | Teddy | 23 | Norway | 15000 |
(4 rows)
looking=# SELECT * FROM COMPANY ORDER BY ID;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
1 | Paul | 32 | California | 20000 | 2001-07-13
3 | Teddy | 23 | Norway | 15000 |
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
(4 rows)
looking=# SELECT * FROM COMPANY ORDER BY SALARY;
id | name | age | address | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
3 | Teddy | 23 | Norway | 15000 |
1 | Paul | 32 | California | 20000 | 2001-07-13
4 | Mark | 25 | Rich-Mond | 65000 | 2007-12-13
5 | David | 27 | Texas | 85000 | 2007-12-13
(4 rows)
GROUP BY
looking=# SELECT * FROM COMPANY;
id | name | age | address | salary
----+-------+-----+----------------------------------------------------+--------
1 | Paul | 32 | California | 20000
2 | Allen | 25 | Texas | 15000
3 | Teddy | 23 | Norway | 20000
4 | Mark | 25 | Rich-Mond | 65000
5 | David | 27 | Texas | 85000
6 | Kim | 22 | South-Hall | 45000
7 | James | 24 | Houston | 10000
8 | Paul | 24 | Houston | 20000
9 | James | 44 | Norway | 5000
10 | James | 45 | Texas | 5000
(10 rows)
looking=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME ORDER BY NAME;
name | sum
-------+-------
Allen | 15000
David | 85000
James | 20000
Kim | 45000
Mark | 65000
Paul | 40000
Teddy | 20000
(7 rows)
looking=# SELECT ADDRESS, SUM(SALARY) FROM COMPANY GROUP BY ADDRESS ORDER BY ADDRESS;
address | sum
----------------------------------------------------+--------
California | 20000
Houston | 30000
Norway | 25000
Rich-Mond | 65000
South-Hall | 45000
Texas | 105000
(6 rows)
HAVING
looking=# select * from company;
LOOKING
id | name | age | address | salary
----+-------+-----+----------------------------------------------------+--------
1 | Paul | 32 | California | 20000
2 | Allen | 25 | Texas | 15000
3 | Teddy | 23 | Norway | 20000
4 | Mark | 25 | Rich-Mond | 65000
5 | David | 27 | Texas | 85000
6 | Kim | 22 | South-Hall | 45000
7 | James | 24 | Houston | 10000
8 | Paul | 24 | Houston | 20000
9 | James | 44 | Norway | 5000
10 | James | 45 | Texas | 5000
(10 rows)
looking=# SELECT NAME FROM COMPANY GROUP BY name HAVING count(name) > 2;
LOOKING
name
-------
James
(1 row)
DISTINCT
looking=# SELECT NAME FROM COMPANY;
LOOKING
name
-------
Paul
Allen
Teddy
Mark
David
Kim
James
Paul
James
James
(10 rows)
looking=# SELECT DISTINCT NAME FROM COMPANY;
LOOKING
name
-------
Teddy
David
Paul
Kim
Mark
Allen
James
(7 rows)
约束
NOT NULL
CREATE TABLE COMPANY1(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);UNIQUE
CREATE TABLE COMPANY3(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL UNIQUE,
ADDRESS CHAR(50),
SALARY REAL DEFAULT 50000.00
);PRIMARY KEY
CREATE TABLE COMPANY4(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);FOREIGN KEY
CREATE TABLE COMPANY6(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);CREATE TABLE DEPARTMENT1(
ID INT PRIMARY KEY NOT NULL,
DEPT CHAR(50) NOT NULL,
EMP_ID INT references COMPANY6(ID)
);CHECK
CREATE TABLE COMPANY5(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL CHECK(SALARY > 0)
);EXCLUSION
EXCLUSION 约束确保如果使用指定的运算符在指定列或表达式上比较任意两行，至少其中一个运算符比较将返回 false 或 null。
CREATE TABLE COMPANY7(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT,
AGE INT ,
ADDRESS CHAR(50),
SALARY REAL,
EXCLUDE USING gist
(NAME WITH =, -- 如果满足 NAME 相同，AGE 不相同则不允许插入，否则允许插入
AGE WITH <>) -- 其比较的结果是如果整个表边式返回 true，则不允许插入，否则允许
);删除约束
ALTER TABLE table_name DROP CONSTRAINT some_name;连接
在 PostgreSQL 中，JOIN 有五种连接类型：
- CROSS JOIN ：交叉连接
- INNER JOIN：内连接
- LEFT OUTER JOIN：左外连接
- RIGHT OUTER JOIN：右外连接
- FULL OUTER JOIN：全外连接
UNION
UNION 操作符用于合并两个或多个 SELECT 语句的结果集。UNION 内部的每个 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时，每个 SELECT 语句中的列的顺序必须相同。
NULL
NULL 值代表遗漏的未知数据。默认地，表的列可以存放 NULL 值。NOT NULL 表示强制字段始终包含值。如果不向字段添加值，就无法插入新记录或者更新记录。具有 NULL 值的字段表示在创建记录时可以留空。NULL 值在查询时可能会导致一些问题，因为一个未知的值去与其他任何值比较，结果永远是未知的。另外无法比较 NULL 和 0，因为它们是不等价的。
looking=# select * from company;
LOOKING
id | name | age | address | salary
----+-------+-----+----------------------------------------------------+--------
1 | Paul | 32 | California | 20000
2 | Allen | 25 | Texas | 15000
3 | Teddy | 23 | Norway | 20000
4 | Mark | 25 | Rich-Mond | 65000
5 | David | 27 | Texas | 85000
6 | Kim | 22 | South-Hall | 45000
7 | James | 24 | Houston | 10000
8 | Paul | 24 | Houston | 20000
9 | James | 44 | Norway | 5000
10 | James | 45 | Texas | 5000
(10 rows)
looking=# UPDATE COMPANY SET ADDRESS = NULL, SALARY = NULL where ID IN(6,7);
UPDATE 2
looking=# select * from company;
LOOKING
id | name | age | address | salary
----+-------+-----+----------------------------------------------------+--------
1 | Paul | 32 | California | 20000
2 | Allen | 25 | Texas | 15000
3 | Teddy | 23 | Norway | 20000
4 | Mark | 25 | Rich-Mond | 65000
5 | David | 27 | Texas | 85000
8 | Paul | 24 | Houston | 20000
9 | James | 44 | Norway | 5000
10 | James | 45 | Texas | 5000
6 | Kim | 22 | |
7 | James | 24 | |
(10 rows)
IS NULL
looking=# select * from company WHERE SALARY IS NULL;
LOOKING
id | name | age | address | salary
----+-------+-----+---------+--------
6 | Kim | 22 | |
7 | James | 24 | |
(2 rows)
IS NOT NULL
looking=# select * from company WHERE SALARY IS NOT NULL;
LOOKING
id | name | age | address | salary
----+-------+-----+----------------------------------------------------+--------
1 | Paul | 32 | California | 20000
2 | Allen | 25 | Texas | 15000
3 | Teddy | 23 | Norway | 20000
4 | Mark | 25 | Rich-Mond | 65000
5 | David | 27 | Texas | 85000
8 | Paul | 24 | Houston | 20000
9 | James | 44 | Norway | 5000
10 | James | 45 | Texas | 5000
(8 rows)
别名
我们可以用 SQL 重命名一张表或者一个字段的名称，这个名称就叫着该表或该字段的别名。创建别名是为了让表名或列名的可读性更强。SQL 中 使用 AS 来创建别名。
表别名
SELECT C.ID, C.NAME, C.AGE, D.DEPT FROM COMPANY AS C, DEPARTMENT AS D WHERE C.ID = D.EMP_ID;列别名
SELECT C.ID AS COMPANY_ID, C.NAME AS COMPANY_NAME, C.AGE, D.DEPT FROM COMPANY AS C, DEPARTMENT AS D WHERE C.ID = D.EMP_ID;触发器
触发器是数据库的回调函数，它会在指定的数据库事件发生时自动执行/调用。
语法
CREATE TRIGGER trigger_name [BEFORE|AFTER] [INSERT|DELETE|UPDATE]
ON table_name
[
-- 触发器逻辑....
];CREATE TRIGGER trigger_name [BEFORE|AFTER] [INSERT|DELETE|UPDATE] OF column_name
ON table_name
[
-- 触发器逻辑....
];实例
创建表
CREATE TABLE COMPANY(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);
CREATE TABLE AUDIT(
EMP_ID INT NOT NULL,
ENTRY_DATE TEXT NOT NULL
);创建触发器
looking=# CREATE OR REPLACE FUNCTION auditlogfunc() RETURNS TRIGGER AS $example_table$
looking$# BEGIN
looking$# INSERT INTO AUDIT(EMP_ID, ENTRY_DATE) VALUES (new.ID, current_timestamp);
looking$# RETURN NEW;
looking$# END;
looking$# $example_table$ LANGUAGE plpgsql;
CREATE FUNCTION
looking=# CREATE TRIGGER example_trigger AFTER INSERT ON COMPANY FOR EACH ROW EXECUTE PROCEDURE auditlogfunc();
CREATE TRIGGER
测试触发器
looking=# INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) VALUES (1, 'Paul', 32, 'California', 20000.00 );
INSERT 0 1
looking=# select * from audit;
LOOKING
emp_id | entry_date
--------+-------------------------------
1 | 2022-06-10 15:01:53.225493+08
(1 row)
列举触发器
looking=# select * from pg_trigger;
LOOKING
oid | tgrelid | tgparentid | tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint | tgdeferrable | tginitdeferred | tgnargs | tgattr | tgargs | tgqual | tgoldtable | tgnewtable
-------+---------+------------+-----------------+--------+--------+-----------+--------------+---------------+---------------+--------------+--------------+----------------+---------+--------+--------+--------+------------+------------
16448 | 16433 | 0 | example_trigger | 16447 | 5 | O | f | 0 | 0 | 0 | f | f | 0 | | \x | | |
(1 row)
looking=# SELECT tgname FROM pg_trigger, pg_class WHERE tgrelid=pg_class.oid AND relname='company';
LOOKING
tgname
-----------------
example_trigger
(1 row)
删除触发器
looking=# DROP TRIGGER EXAMPLE_TRIGGER ON COMPANY;
DROP TRIGGER
索引
索引必须是在 WHERE 子句的过滤条件中使用非常频繁的列。
语法
CREATE INDEX index_name ON table_name;单列索引
CREATE INDEX index_name ON table_name (column_name);组合索引
CREATE INDEX index_name ON table_name (column1_name, column2_name);唯一索引
局部索引 是在表的子集上构建的索引；子集由一个条件表达式上定义。索引只包含满足条件的行。
CREATE UNIQUE INDEX index_name ON table_name (column_name);局部索引
CREATE INDEX index_name ON table_name (conditional_expression);隐式索引
隐式索引 是在创建对象时，由数据库服务器自动创建的索引。索引自动创建为主键约束和唯一约束。
查看索引
查看表索引
\d 查看数据库所有索引
\di删除索引
DROP INDEX index_name;使用准则
使用索引时，需要考虑下列准则：
- 索引不应该使用在较小的表上。
- 索引不应该使用在有频繁的大批量的更新或插入操作的表上。
- 索引不应该使用在含有大量的 NULL 值的列上。
- 索引不应该使用在频繁更新操作的列上。
ALTER TABLE
语法
用 ALTER TABLE 在一张已存在的表上添加列的语法如下：
ALTER TABLE table_name ADD column_name datatype;在一张已存在的表上 DROP COLUMN（删除列），语法如下：
ALTER TABLE table_name DROP COLUMN column_name;修改表中某列的 DATA TYPE（数据类型），语法如下：
ALTER TABLE table_name ALTER COLUMN column_name TYPE datatype;给表中某列添加 NOT NULL 约束，语法如下：
ALTER TABLE table_name ALTER column_name datatype NOT NULL;给表中某列 ADD UNIQUE CONSTRAINT（ 添加 UNIQUE 约束），语法如下：
ALTER TABLE table_name ADD CONSTRAINT MyUniqueConstraint UNIQUE(column1, column2...);给表中 ADD CHECK CONSTRAINT（添加 CHECK 约束），语法如下：
ALTER TABLE table_name ADD CONSTRAINT MyUniqueConstraint CHECK (CONDITION);给表 ADD PRIMARY KEY（添加主键），语法如下：
ALTER TABLE table_name ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2...);DROP CONSTRAINT （删除约束），语法如下：
ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint;DROP PRIMARY KEY （删除主键），语法如下：
ALTER TABLE table_name DROP CONSTRAINT MyPrimaryKey;实例
添加列：
looking=# select * from company;
LOOKING
id | name | age | address | salary
----+------+-----+----------------------------------------------------+--------
1 | Paul | 32 | California | 20000
(1 row)
looking=# alter table company add gender char(1);
ALTER TABLE
looking=# select * from company;
LOOKING
id | name | age | address | salary | gender
----+------+-----+----------------------------------------------------+--------+--------
1 | Paul | 32 | California | 20000 |
(1 row)
删除列：
looking=# select * from company;
LOOKING
id | name | age | address | salary | gender
----+------+-----+----------------------------------------------------+--------+--------
1 | Paul | 32 | California | 20000 |
(1 row)
looking=# alter table company drop gender;
ALTER TABLE
looking=# select * from company;
LOOKING
id | name | age | address | salary
----+------+-----+----------------------------------------------------+--------
1 | Paul | 32 | California | 20000
(1 row)
添加和删除 NOT NULL 约束
looking=# alter table company alter column salary set not null;
ALTER TABLE
looking=# alter table company alter column salary drop not null;
ALTER TABLE
TRUNCATE TABLE
TRUNCATE TABLE 用于删除表的数据，但不删除表结构，DELETE 也可以删除表数据，但是它会扫描表，所以速度比 TRUNCATE 慢。TRUNCATE TABLE 可以立即释放表空间，而不需要后续 VACUUM 操作（与 SQLite 的 VACUUM 操作类似），这在大型表上非常有用。也可以用 DROP TABLE 删除表，但是这个命令会连表的结构一起删除，如果想插入数据，需要重新建立这张表。
DELETE
looking=# delete from company;
DELETE 1
TRUNCATE
looking=# truncate table company;
TRUNCATE TABLE
DROP
looking=# drop table company;
DROP TABLE
视图
同 MySQL。
事务
- BEGIN 或 BEGIN TRANSACTION 开始一个事务
- ROLLBACK 事务回滚
- COMMIT 或 END TRANSACTION 事务确认
锁
looking=# begin;
BEGIN
looking=# LOCK TABLE company IN ACCESS EXCLUSIVE MODE;
LOCK TABLE
looking=# do something on company;
looking=# commit;
COMMIT
上面的消息指示表被锁定，直到事务结束，并且要完成事务，您必须回滚或提交事务。
子查询
也叫嵌套查询，同 MySQL。
SELECT
INSERT INTO COMPANY_BKP SELECT * FROM COMPANY WHERE ID IN (SELECT ID FROM COMPANY) ;UPDATE
UPDATE COMPANY SET SALARY = SALARY * 0.50 WHERE AGE IN (SELECT AGE FROM COMPANY_BKP WHERE AGE >= 35 ); -- 薪资减半？DELETE
DELETE FROM COMPANY WHERE AGE IN (SELECT AGE FROM COMPANY_BKP WHERE AGE > 35 ); -- 裁员？AUTO INCREMENT
MySQL
CREATE TABLE IF NOT EXISTS `runoob_tbl`(
`runoob_id` INT UNSIGNED AUTO_INCREMENT,
`runoob_title` VARCHAR(100) NOT NULL,
`runoob_author` VARCHAR(40) NOT NULL,
`submission_date` DATE,
PRIMARY KEY ( `runoob_id` )
)ENGINE=InnoDB DEFAULT CHARSET=utf8;PostgreSQL
CREATE TABLE COMPANY(
ID SERIAL PRIMARY KEY,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);SMALLSERIAL、SERIAL 和 BIGSERIAL 范围：
| 伪类型 | 存储大小 | 范围 |
|---|---|---|
SMALLSERIAL |
2字节 | 1 到 32,767 |
SERIAL |
4字节 | 1 到 2,147,483,647 |
BIGSERIAL |
8字节 | 1 到 922,337,2036,854,775,807 |