Mysql数据库二:表的增删改查

----建表
CREATE TABLE emp(
id int PRIMARY key auto_increment,
name char(10) ,
birthday DATE ,
salary FLOAT (7,2)
)CHARACTER SET utf8;

----插入
INSERT emp (name,birthday,salary) VALUES ("egon","1991-1-1",20000),
("alex","1992-1-1",2000),
("peiqi","1998-3-1",30000);

INSERT emp SET name="yuan",salary="66666";

----修改
UPDATE emp set name = "egon1" WHERE id=1;
UPDATE emp set name="ALex",salary=55555 WHERE name="alex";
UPDATE emp set salary=salary+10000 where name = "egon1";

----删除
DELETE FROM emp WHERE name = "Alex";
DELETE FROM emp; ---清除表内容,但是auto_increment没有被重置就是说再插入数据id还是会自增
truncate table emp; ---id自增被删除,等价于完完全全清空表.

-------------------查找--------------------------

---准备表
CREATE TABLE exam(

id INT PRIMARY KEY auto_increment,
name VARCHAR (20),
JS DOUBLE ,
Django DOUBLE ,
分显示
SELECT name,JS+Django+OpenStack from exam;
SELECT name as 姓名,JS+Django+OpenStack as 总成绩 from exam;
SELECT name,JS+Django+OpenStack 总成绩 from exam;

---使用where子句过滤查询

-- where字句中可以使用：

-- 比较运算符：
> < >= <= <> !=
到20之间
或20或30
like 'yuan%'
/*
pattern可以是%或者_，
如果是%则表示任意多字符，此例如唐僧,唐国强
如果是_则表示一个字符唐_，只有唐僧符合。两个_则表示两个字符：__
*/

-- 逻辑运算符
和100是闭区间
SELECT * from exam where js in (88,86);
SELECT * from exam where name like "yu%";
SELECT * from exam where js>90 and django > 90;

---order by 排序
-- Asc 升序、Desc 降序，其中asc为默认值 ORDER BY 子句应位于SELECT语句的结尾。
SELECT * from exam ORDER BY js;
SELECT * FROM exam ORDER BY js desc; --降序
select name ,(ifnull(JS,0)+ifnull(Django,0)+ifnull(OpenStack,0))
总成绩
from exam order by 总成绩 desc;

select name ,(ifnull(JS,0)+ifnull(Django,0)+ifnull(OpenStack,0))
总成绩
from exam where name like 'a%'
条记录
select * from exam limit 2,2;

---正则表达式
SELECT * from exam where name regexp "^a";
select * from exam WHERE name REGEXP "[a-z]{5}";
SELECT * from exam WHERE name regexp "n$";
SELECT * FROM exam WHERE name regexp "m{2}";

------------------group by分组查询---------------------
---准备表和数据
CREATE TABLE menu(
id INT PRIMARY KEY auto_increment,
product_name VARCHAR (20),
price FLOAT(6,2),
born_date DATE,
class VARCHAR (20)
);

INSERT INTO menu (product_name,price,born_date,class) VALUES
("苹果",20,20170612,"水果"),
("香蕉",80,20170602,"水果"),
("水壶",120,20170612,"电器"),
("被罩",70,20170612,"床上用品"),
("音响",420,20170612,"电器"),
("床单",55,20170612,"床上用品"),
("草莓",34,20170612,"水果");

SELECT * from menu GROUP BY 4; -- 按位置字段筛选,此时按照date筛选
select class ,SUM(price) from menu group by class;
SELECT class,sum(price) from menu GROUP BY class HAVING sum(price)>150;
/*
having 和 where两者都可以对查询结果进行进一步的过滤，差别有：
<1>where语句只能用在分组之前的筛选，having可以用在分组之后的筛选；
<2>使用where语句的地方都可以用having进行替换
<3>having中可以用聚合函数，where中就不行。
*/
SELECT * from menu HAVING class = "水果";
SELECT class,count(id) from menu group by class;--先按class分组然后统计每组中的个数
result:
+----------+--------------+
| class | count(price) |
+----------+--------------+
| 床上用品 | 2 |
| 水果 | 3 |
| 电器 | 2 |
+----------+--------------+