数据库模糊查询知识点和例题MySQL

模糊查询

1.like

一般搭配着通配符使用，用作字符型的判断
通配符：% 任意多个字符;_ 任意单个字符 1
例题：
#例1：查询姓名中包含字符 e的员工信息
SELECT * FROM employees WHERE last_name LIKE ‘%e%’;
#例2：查询姓名中第二个字符为e，第四个字符为a的员工信息
SELECT * FROM employees WHERE last_name LIKE ’_e_a%’;
#例3：查询姓名中第三个字符为_的员工信息
SELECT * FROM employees WHERE last_name LIKE ‘___%’;
#ESCAPE 自定义 转移符
SELECT * FROM employees WHERE last_name LIKE ‘__KaTeX parse error: Expected group after '_' at position 1: _̲%' ESCAPE '’;
// ESCAPE ’′;这句话是让'; 这句话是 让′;这句话是让 拥有转义字符的形式和功能
UPDATE employees SET last_name=’’ ‘’ WHERE employee_id=100;

2.between and

特点：在…之间
①等价于 使用 字段>=值1 and 字段<=值2
②两个临界值是包含的 [1,10]
③两个临界值不能颠倒顺序
#例1：显示出表employees部门编号在80-100之间 的姓名、职位
SELECT last_name,job_id,department_id FROM employees WHERE department_id BETWEEN 80 AND 100;
WHERE department_id BETWEEN 100 AND 80; ×
#等价于
SELECT last_name,job_id,department_id FROM employees WHERE department_id<=100 AND department_id>=80;

3.in

特点：判断某个字段的值是否在某个列表内
in(值1，值2，…)等价于 or
#例1：显示出表employees的manager_id 是 100,101,110 的员工姓名、职位
SELECT last_name,job_id,manager_id FROM employees WHERE manager_id IN(100,101,110);
#等价于
SELECT last_name,job_id,manager_id FROM employees WHERE manager_id=100 OR manager_id=101 OR manager_id = 110;
#例2：查询 job_id 为AD_VP或ST_MAN或SA_MAN
SELECT last_name,job_id,manager_id FROM employees WHERE job_id IN(‘AD_VP’,‘S__MAN’);# ×

4.is null/is not null

#例1：查询没有奖金的员工
SELECT * FROM employees WHERE commission_pct IS NULL;
#案例2：查询有奖金的员工
SELECT * FROM employees WHERE commission_pct IS NOT NULL;
例题：
#2.查询员工号为176的员工的姓名和部门号和年薪
SELECT ***FNULL(commission_pct,0)**,commission_pct FROM employees;
SELECT last_name,department_id,salary12 (1+IFNULL(commission_pct,0)) 年薪
FROM employees WHERE employee_id=176;
选择在***20或50***号部门工作的员工姓名和部门号
SELECT last_name,department_id FROM employees WHERE department_id ***IN(20,50)***;
#选择姓名中有字母a和e的员工姓名
SELECT last_name FROM employees WHERE last_name LIKE ‘%a%’ AND last_name LIKE ‘%e%’;
#或
SELECT last_name FROM employees WHERE last_name LIKE ‘%a%e%’ OR last_name LIKE ‘%e%a%’;