Mysql-DML(数据处理语言)

-- 插入数据
insert into member values(1,'张三',21,5000);
insert into member(id,name) values(2,'李四');
insert into member values(3,'王五',23,3000)
,(4,'纪六',24,4000)
,(5,'查七',25,5000);
-- 更新（修改数据) 不加限制条件 该字段全部修改
update member set age= 30 where id=1; 
-- 删除数据

delete from member where name='王五';

-- 查询数据
-- 全查询
select * from member;
-- 部分查询 别名 as
select id as '卡号'
,name as '姓名'
from member;
-- 在字段中计算
select name ,salary+500 from member;
-- 条件查询
select * from member where salary = 4000;
-- 去重
select distinct * from member;
select * from member group by id;
-- 筛选条件 where
-- 比较运算符 > < >= <= != <>

select * from member where salary != 4000;
-- 逻辑运算符     and or not 
select * from member where salary !=  4000 and id > 3;
-- 在。。范围
-- in（a,b） not in（） a和b
SELECT * FROM member where age  in(21,24);
-- between a and b    a到b 
SELECT * FROM member where age BETWEEN 21 and 24;
-- 判断是否为空 is null/is not null
SELECT * FROM member where age  is  null;
-- 模糊查询  _匹配任意字符（占位符） %0或多个
SELECT * FROM member where name like '%六';

-- 分页 LIMIT（a）查看前a行，LIMIT（a,b）从查询的结果从第a个下标开始查看b行

-- m条，n页
-- SELECT * FROM student LIMIT m*(n-1),m; 

-- 排序 ORDER BY 字段名 ASC -- 升序 DESC -- 降序

SELECT * FROM student ORDER BY  score  DESC,id desc; 

-- 聚合函数
-- 统计次数 COUNT(*) 
SELECT COUNT(*) FROM student ;
-- 求和 SUM
SELECT SUM(score) FROM student ;
-- 最大值 max
SELECT max(score) FROM student ;
-- 最小值 min
SELECT min(score) FROM student ;
-- 平均值 avg
SELECT avg(score) FROM student ;

-- 分组 group by 只能查询group by后的普通字段 和聚合函数

SELECT  class,max(score) as max_score  from student GROUP BY class HAVING  max_score>=90;

-- where不能跟分组后面 ，having只能在分组里面
-- where后面不能有聚合函数，hiving可以

-- SELECT *,指定列，as 别名，聚合函数
-- from 表格名
-- where 逻辑运算符
-- group by 分组
-- having 分组后筛选
-- order by 排序（asc/desc）