进阶二:条件查询
语法:
select 查询列表 from 表名 where 筛选条件;
执行顺序:
①from子句
②where子句
③select子句
select last_name,first_name from employees where salary>20000;
特点:
- 1、按关系表达式筛选
关系运算符:> < >= <= = <>
补充:也可以使用!=,但不建议 - 2、按逻辑表达式筛选
逻辑运算符:and or not
补充:也可以使用&& || ! ,但不建议 - 3、模糊查询
like
in
between and
is null
一、按关系表达式筛选
#案例1:查询部门编号不是100的员工信息
SELECT *
FROM employees
WHERE department_id <> 100;
#案例2:查询工资<15000的姓名、工资
SELECT last_name,salary
FROM employees
WHERE salary<15000;
二、按逻辑表达式筛选
#案例1:查询部门编号不是 50-100之间员工姓名、部门编号、邮箱
#方式1:
SELECT last_name,department_id,email
FROM employees
WHERE department_id <50 OR department_id>100;
#方式2:
SELECT last_name,department_id,email
FROM employees
WHERE NOT(department_id>=50 AND department_id<=100);
#案例2:查询奖金率>0.03 或者 员工编号在60-110之间的员工信息
SELECT *
FROM employees
WHERE commission_pct>0.03 OR (employee_id >=60 AND employee_id<=110);
三、模糊查询
1、like
功能:一般和通配符搭配使用,对字符型数据进行部分匹配查询
常见的通配符:
_
任意单个字符
%
任意多个字符,支持0-多个
like/not like
#案例1:查询姓名中包含字符a的员工信息
SELECT *
FROM employees
WHERE last_name LIKE '%a%';
#案例2:查询姓名中包含最后一个字符为e的员工信息
SELECT *
FROM employees
WHERE last_name LIKE '%e';
#案例3:查询姓名中包含第一个字符为e的员工信息
SELECT *
FROM employees
WHERE last_name LIKE 'e%';
#案例4:查询姓名中包含第三个字符为x的员工信息
SELECT *
FROM employees
WHERE last_name LIKE '__x%';
#案例5:查询姓名中包含第二个字符为_的员工信息
SELECT *
FROM employees
WHERE last_name LIKE '_\_%';
SELECT *
FROM employees
WHERE last_name LIKE '_$_%' ESCAPE '$';
##### 2、in
功能:查询某字段的值是否属于指定的列表之内
`a in(常量值1,常量值2,常量值3,...)`
`a not in(常量值1,常量值2,常量值3,...)`
`in/not in`
```sql
#案例1:查询部门编号是30/50/90的员工名、部门编号
#方式1:
SELECT last_name,department_id
FROM employees
WHERE department_id IN(30,50,90);
#方式2:
SELECT last_name,department_id
FROM employees
WHERE department_id = 30
OR department_id = 50
OR department_id = 90;
#案例2:查询工种编号不是SH_CLERK或IT_PROG的员工信息
#方式1:
SELECT *
FROM employees
WHERE job_id NOT IN('SH_CLERK','IT_PROG');
#方式2:
SELECT *
FROM employees
WHERE NOT(job_id ='SH_CLERK'
OR job_id = 'IT_PROG');
3、between and
功能:判断某个字段的值是否介于xx之间
between and/not between and
#案例1:查询部门编号是30-90之间的部门编号、员工姓名
#方式1:
SELECT department_id,last_name
FROM employees
WHERE department_id BETWEEN 30 AND 90;
#方式2:
SELECT department_id,last_name
FROM employees
WHERE department_id>=30 AND department_id<=90;
#案例2:查询年薪不是100000-200000之间的员工姓名、工资、年薪
SELECT last_name,salary,salary*12*(1+IFNULL(commission_pct,0)) 年薪
FROM employees
WHERE salary*12*(1+IFNULL(commission_pct,0))<100000 OR salary*12*(1+IFNULL(commission_pct,0))>200000;
SELECT last_name,salary,salary*12*(1+IFNULL(commission_pct,0)) 年薪
FROM employees
WHERE salary*12*(1+IFNULL(commission_pct,0)) NOT BETWEEN 100000 AND 200000;
4、is null/is not null
#案例1:查询没有奖金的员工信息
SELECT *
FROM employees
WHERE commission_pct IS NULL;
#案例2:查询有奖金的员工信息
SELECT *
FROM employees
WHERE commission_pct IS NOT NULL;
SELECT *
FROM employees
WHERE salary IS 10000;
对比
=
只能判断普通的内容
IS
只能判断NULL值
<=>
安全等于,既能判断普通内容,又能判断NULL值
SELECT *
FROM employees
WHERE salary <=> 10000;
SELECT *
FROM employees
WHERE commission_pct <=> NULL;