MySQL基础练习

MySQL 基础
#1.查询常量
SELECT 100;

SELECT last_name FROM employees;

#4.查询多个字段
SELECT last_name,email,employee_id FROM employees;

#5.查询所有字段
SELECT * FROM employees;

F12 :对齐格式
SELECT
last_name,
email,
job_id

#6.查询函数（调用函数，获取返回值）
SELECT DATABASE();
SELECT VERSION();
SELECT USER();

#7.起别名
#方式一：使用as关键字

SELECT USER() AS 用户名;

SELECT last_name AS ‘姓 名’ FROM employees;

#方式二：空格

#八，
– 需求 ： 查询 first_name 和 last_name 拼接成的全名，最终起别名为：姓 名

SELECT CONCAT(first_name,last_name) AS ‘姓 名’ FROM employees;

SELECT first_name,last_name FROM employees;

#9. distinct的使用 去重
#需求： 查询员工涉及到的部门编号有哪些

SELECT DISTINCT department_id FROM employees;

#10.查看表的结构
DESC employees;
SHOW COLUMNS FROM employees;

---

#进阶二：条件查询
/*
语法：
select 查询列表
frmo 表名
where 筛选条件

执行顺序：

1. from子句
   2.where子句
   3.select 子句

select last_name,first_name from emp where salary > 20000;

*/

#1.按关系表达式筛选
#案例一，查询部门编号不是100的员工信息
SELECT * FROM employees WHERE department_id <> 100;

#案例二： 查询工资<15000的姓名，工资
SELECT CONCAT(last_name,first_name) AS ‘姓名’ 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
#方式一：
SELECT last_name,department_id,email FROM employees WHERE department_id<50 OR department_id>100;

#方式二：
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);

---

#1.like

#案例一：查询姓名中包含最后一个字符为e的员工的信息
SELECT * FROM employees WHERE last_name LIKE ‘%a%’;

#案例二：查询姓名中包含第一个字符为e的员工的信息
SELECT * FROM employees WHERE last_name LIKE ‘e%’;

#案例三：查询姓名中包含第三个字符为e的员工的信息
SELECT * FROM employees WHERE last_name LIKE ‘___x%’;

#案例四：查询姓名中包含第二个字符为_的员工的信息
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1，常量2.常量3…)
a not in(常量1，常量2.常量3…)

in/ not in

*/

#案例一：查询部门编号是 30/50/90的员工名和部门编号
SELECT last_name,department_id FROM employees
WHERE department_id IN(30,50,90);

#案例二：查询工种编号不是SH_CLERK 或 IT_PROG的员工信息
SELECT * FROM employees WHERE (job_id != ‘SH_CLERK’) AND (job_id != ‘IT_PROG’);

SELECT * FROM employees WHERE job_id NOT IN(‘SH_CLERK’,‘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

*/

#案例一： 查询部门编号是30-90之间的部门编号，员工姓名
SELECT department_id,last_name FROM employees
WHERE department_id>=30 AND department_id<=90;

SELECT department_id,last_name FROM employees
WHERE department_id BETWEEN 30 AND 90;

#案例二： 查询年薪不是100000-200000直接员工的姓名，工资，年薪
SELECT last_name,salary,salary12(IFNULL(commission_pct,0)+1) 年薪
FROM employees
WHERE salary12(IFNULL(commission_pct,0)+1) NOT BETWEEN 100000 AND 200000;

SELECT last_name,salary,salary12(IFNULL(commission_pct,0)+1) AS 年薪
FROM employees
WHERE salary12(IFNULL(commission_pct,0)+1)<100000 OR salary12(IFNULL(commission_pct,0)+1)>200000;

#4. is null / is not null

#案例一：查询没有奖金的员工信息
SELECT * FROM employees WHERE commission_pct IS NULL;

#案例一：查询有奖金的员工信息
SELECT * FROM employees WHERE commission_pct IS NOT NULL;

#1.查询工资大于 12000 的员工姓名和工资
SELECT last_name,salary FROM employees WHERE salary > 12000;

#2.查询员工号为176的员工姓名和部门号和年薪
SELECT last_name,department_id,salary12(IFNULL(commission_pct,0)+1) 年薪
FROM employees
WHERE employee_id = 176;

#3.选择工资不在 5000 到 12000 的员工姓名 和 工资
SELECT last_name,salary FROM employees
WHERE salary NOT BETWEEN 5000 AND 12000;

#方式二：
SELECT last_name,salary FROM employees
WHERE NOT(salary>=5000 AND salary<=12000);

#方式三：
SELECT last_name,salary FROM employees
WHERE salary<5000 OR salary>12000;

#4.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=20 OR department_id=50;

#方式二
SELECT last_name,department_id FROM employees
WHERE department_id IN(20,50);

#5.选择公司中没有管理者的员工姓名及 job_id
SELECT last_name,job_id FROM employees
WHERE manager_id IS NULL;

#6. 选择公司中有奖金的员工姓名，工资和奖金级别
SELECT last_name,salary,commission_pct FROM employees
WHERE commission_pct IS NOT NULL;

#7.选择员工姓名的第三个字母是a的员工姓名
SELECT last_name FROM employees
WHERE last_name LIKE ‘__a%’;

#8.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%’;

#9.显示出表 employees 表中 first_name 以‘e’结尾的员工信息
SELECT * FROM employees
WHERE first_name LIKE ‘%e’;

#10.显示出表 employees 部门编号在 80-100 之间的姓名 职位
SELECT last_name,job_id FROM employees
WHERE department_id BETWEEN 80 AND 100;

#方式二：
SELECT last_name,job_id FROM employees
WHERE department_id>=80 AND department_id<=100;

#11.显示出表 employees 的 manager_id 是100，101,110的员工姓名，职位
SELECT last_name,job_id FROM employees
WHERE manager_id IN(100,101,110);

SELECT last_name,job_id FROM employees
WHERE manager_id=100 OR manager_id=101 OR manager_id=110;