1.分类

算术运算符
比较运算符
逻辑运算符
按位运算符
2.算数运算符
集中常见的算数运算符，假设a=2,b=4;

运算符	描述	示例
+	加
-	减
*	乘
/	除（取整）	b/a = 2
%	模（取余）	b%a=0
^	指数	a^b=16

示例

runoobdb=# select 2+3;
 ?column?
----------
        5
(1 行记录)
runoobdb=# select 2*3;
 ?column?
----------
        6
(1 行记录)
runoobdb=# select 4/2;
 ?column?
----------
        2
(1 行记录)
runoobdb=# select 12%5;
 ?column?
----------
        2
(1 行记录)
runoobdb=# select 2^3;
 ?column?
----------
        8
(1 行记录)

3.比较运算符

假设变量a=1，变量b等于2;

运算符	描述	示例
=	等于	(a=b)为false
!=	不等于	（a!=b）为true
<>	不等于	（a<>b）为true
>	大于	（a>b）为false
<	小于	（a<b）为true
>=	大于等于	(a>=b)为false
<=	小于等于	（a<=b）为true

4.示例

创建company表，可由company.sql导入；

runoobdb=# 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
(7 行记录)

读取 SALARY 字段大于 50000 的数据；

runoobdb=# SELECT * FROM company WHERE SALARY > 50000;
 id | name  | age |                      address                       | salary
----+-------+-----+----------------------------------------------------+--------
  4 | Mark  |  25 | Rich-Mond                                          |  65000
  5 | David |  27 | Texas                                              |  85000
(2 行记录)

读取 SALARY 字段等于 20000 的数据：

runoobdb=# SELECT * FROM company WHERE SALARY = 20000;
 id | name  | age |                      address                       | salary
----+-------+-----+----------------------------------------------------+--------
  1 | Paul  |  32 | California                                         |  20000
  3 | Teddy |  23 | Norway                                             |  20000
(2 行记录)

读取 SALARY 字段不等于 20000 的数据：

runoobdb=# SELECT * FROM company WHERE SALARY !=20000;
 id | name  | age |                      address                       | salary
----+-------+-----+----------------------------------------------------+--------
  2 | Allen |  25 | Texas                                              |  15000
  4 | Mark  |  25 | Rich-Mond                                          |  65000
  5 | David |  27 | Texas                                              |  85000
  6 | Kim   |  22 | South-Hall                                         |  45000
  7 | James |  24 | Houston                                            |  10000
(5 行记录)


runoobdb=# SELECT * FROM company WHERE SALARY <> 20000;
 id | name  | age |                      address                       | salary
----+-------+-----+----------------------------------------------------+--------
  2 | Allen |  25 | Texas                                              |  15000
  4 | Mark  |  25 | Rich-Mond                                          |  65000
  5 | David |  27 | Texas                                              |  85000
  6 | Kim   |  22 | South-Hall                                         |  45000
  7 | James |  24 | Houston                                            |  10000
(5 行记录)

读取 SALARY 字段大于等于 65000 的数据：

runoobdb=# select * from company where salary > 65000;
 id | name  | age |                      address                       | salary
----+-------+-----+----------------------------------------------------+--------
  5 | David |  27 | Texas                                              |  85000
(1 行记录)

5.逻辑运算符

运算符	描述
AND	如果两个操作数都非零，则条件为真； PostgresSQL 中的 WHERE 语句可以用 AND 包含多个过滤条件。
NOT	如果条件为真则逻辑非运算符将使其为假； PostgresSQL 有 NOT EXISTS, NOT BETWEEN, NOT IN 等运算符
OR	如果两个操作数中有任意一个非零，则条件为真。 PostgresSQL 中的 WHERE 语句可以用 OR 包含多个过滤条件。

6.示例

读取 AGE 字段大于等于 25 且 SALARY 字段大于等于 6500 的数据：

runoobdb=# select * from company where age >= 25 and salary >= 6500;
 id | name  | age |                      address                       | salary
----+-------+-----+----------------------------------------------------+--------
  1 | Paul  |  32 | California                                         |  20000
  2 | Allen |  25 | Texas                                              |  15000
  4 | Mark  |  25 | Rich-Mond                                          |  65000
  5 | David |  27 | Texas                                              |  85000
(4 行记录)

读取 AGE 字段大于等于 25 或 SALARY 字段大于 6500 的数据：

runoobdb=# SELECT * FROM COMPANY WHERE AGE >= 25 OR SALARY >= 6500;
 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
(7 行记录)

读取 SALARY 字段不为 NULL 的数据：

runoobdb=# SELECT * FROM company WHERE salary IS NOT NULL;
 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
(7 行记录)

PostgreSQL

七、运算符

1.分类

2.算数运算符

3.比较运算符

4.示例

5.逻辑运算符

6.示例