通配符不等代表null

条件查询

select 查询列表 from 表名 where 筛选条件;

分类:

按条件表达式筛选 =，！=
按逻辑表达式筛选 and or not
模糊查询 like、between and、in、is null

查询工资大于12000的员工信息

SELECT * FROM employees WHERE salary >12000;

查询部门编号不等90的员工名和部门编号,要查询的编号

SELECT last_name,department_id FROM employees WHERE department_id <>90;

按逻辑表达式筛选

查询工资在10000到20000之间的员工名、工资以及奖金

SELECT last_name ,salary,commission_pct FROM employees WHERE salary<20000
AND salary>10000;

查询部门编号不是在90到110之间，或者工资高于15000的员工

SELECT
    *
FROM employees
WHERE department_id <90 
OR  department_id >110
OR      salary>15000;
#或者
SELECT *
FROM employees
WHERE  NOT(department_id>=90 AND department_id<=110) OR salary>15000;

#查找员工姓名和工资不在8000到17000，且按工资升序排列

SELECT
    last_name,
    salary
FROM
    employees
WHERE
 salary NOT  BETWEEN 8000 AND 17000
ORDER BY
    salary ASC;

模糊查询
like,查询员工名中包含字符a的员工信息

SELECT 
    *
FROM 
    employees
WHERE
    last_name LIKE '%a%';   //百分号%是通配字符,代表其他任意多个字符，_代表任意一个字符

案例:查询员工名中第三个字符为e，第五个字符为a的员工名和工资

SELECT 
    last_name,
    salary
FROM employees
WHERE 
    last_name LIKE '__e_a%';  //2个下划线+e+一个下划线+a

案例：查询员工名中第二个字符为_的员工名,正常转义字符\

SELECT 
    last_name
FROM 
    employees
WHERE
    last_name LIKE '_\_%';

自定义转义字符

SELECT 
    last_name
FROM 
    employees
WHERE
    last_name LIKE'_@_%' ESCAPE '@';