like语法：select * from table_name where c1 like regex(正则表达式)常见正则表达式：*:[通配符]，可以匹配所有/任意字符%:[占位符],[占位]%:作用是帮别人占位。特点是帮忙占座的人不确定到底会不会来\n:[换行符] 换行\t:[制表符] tab键?: 匹配出现0次或1次任意字符
以下哪些正确？哪些错误？
%马%：能查询出来，正确的，因为%：特点：多个或一个，也可以没有。出现【马】这个字，就匹配
%%...马%%...：能查询出来，有问题，出现【马】这个字，就匹配
马%：能查询出来，正确的，以【马】这个字开头，就匹配
马%%：能查询出来，有问题，以【马】这个字开头，就匹配
马n%：能查询出来，有问题，以【马】这个字开头，就匹配
【select * from b2_student_info where sname like '%马%';】
【select * from b2_student_info where sname like '%%马%';】
【select * from b2_student_info where sname like '%马%%';】
【select * from b2_student_info where sname like '%%马%%';】
【select * from b2_student_info where sname like '马%';】
【select * from b2_student_info where sname like '马%%';】
【select * from b2_student_info where sname like '马%%%';】
select sum(b2bigdatascore) from b2_score_info;select sum(b2databasescore) from b2_score_info;select avg(b2bigdatascore) from b2_score_info;select avg(b2bigdatascore) from b2_score_info;select max(b2bigdatascore) from b2_score_info;select min(b2bigdatascore) from b2_score_info;select max(b2bigdatascore) from b2_score_info;select min(b2bigdatascore) from b2_score_info;
简化写法
select sum(b2bigdatascore),avg(b2bigdatascore),max(b2bigdatascore),min(b2bigdatascore),sum(b2databasescore),avg(b2databasescore),max(b2databasescore),min(b2databasescore) from b2_score_info;
select c1 as bm1,c2 as bm2,c3 as bm3...from table _name;select function(c1) as bm1,function(c2) as bm2,function(c3) as bm3 ... from table name where condition;
需求七：针对【select sum(b2bigdatascore),avg(b2bigdatascore),max(b2bigdatascore),min(b2bigdatascore),sum(b2databasescore),avg(b2databasescore),max(b2databasescore),min(b2databasescore) from b2_score_info;】这条简化后的SQL，给每个查询后的字段取对应的【别名】。
命令：
select sum(b2bigdatascore) as sumOfBDS,avg(b2bigdatascore) as avgOfBDS,max(b2bigdatascore) as maxOfBDS,min(b2bigdatascore) as minOfBDS,sum(b2databasescore) sumOfDBS,avg(b2databasescore) as avgOfDBS,max(b2databasescore) as maxOfDBS,min(b2databasescore) as minOfDBS from b2_score_info;
需求八：求所有姓张的同学的【总分】、【平均分】、【最高分】以及【最低分】
需求九：求所有姓马的同学的【总分】、【平均分】、【最高分】以及【最低分】
需求十：求所有姓刘的同学的【总分】、【平均分】、【最高分】以及【最低分】
命令：
select sum(b2bigdatascore),avg(b2bigdatascore),max(b2bigdatascore),min(b2bigdatascore) from b2_score_info where sname like '张%';select sum(b2bigdatascore),avg(b2bigdatascore),max(b2bigdatascore),min(b2bigdatascore) from b2_score_info where sname like '马%';select sum(b2bigdatascore),avg(b2bigdatascore),max(b2bigdatascore),min(b2bigdatascore) from b2_score_info where sname like '刘%';
需求十一：
通过【as】取别名来解决名字长
命令：
select sum(b2bigdatascore) as sumOfBDS,avg(b2bigdatascore) as avgOfBDS,max(b2bigdatascore) as maxOfBDS,min(b2bigdatascore) as minOfBDS from b2_score_info where sname like '张%';select sum(b2bigdatascore) as sumOfBDS,avg(b2bigdatascore) as avgOfBDS,max(b2bigdatascore) as maxOfBDS,min(b2bigdatascore) as minOfBDSfrom b2_score_info where sname like '马%';select sum(b2bigdatascore) as sumOfBDS,avg(b2bigdatascore) as avgOfBDS,max(b2bigdatascore) as maxOfBDS,min(b2bigdatascore) as minOfBDS from b2_score_info where sname like '刘%';
select sum(b2bigdatascore) as sumOfBDS,avg(b2bigdatascore) as avgOfBDS,max(b2bigdatascore) as maxOfBDS,min(b2bigdatascore) as minOfBDS from b2_score_info where sname like '张%' or sname like '马%' or sname like '刘%';
ASCII (American Standard Code for Information Interchange)：美国信息交换标准代码是基于拉丁字母的一套电脑编码系统，主要用于显示现代英语和其他西欧语言。它是最通用的信息交换标准，并等同于国际标准 ISO/IEC 646。ASCII第一次以规范标准的类型发表是在1967年，最后一次更新则是在1986年，到目前为止共定义了128个字符 [1]。
insert into table_name(c1,c2,c3...) values(v1,v2,v3...),(v1,v2,v3...),...;
-- 查看表记录：select * from t_student;-- 在t_student数据库表中插入数据：insert into t_student values (1,'张三','男',18,'2022-5-8','软件1班','123@126.com');insert into t_student values (10010010,'张三','男',18,'2022-5-8','软件1班','123@126.com');insert into t_student values (2,'张三','男',18,'2022.5.8','软件1班','123@126.com');insert into t_student values (2,"张三",'男',18,'2022.5.8','软件1班','123@126.com');insert into t_student values (7,"张三",'男',18,now(),'软件1班','123@126.com');insert into t_student values (9,"易烊千玺",'男',18,now(),'软件1班','123@126.com');insert into t_student (sno,sname,enterdate) values (10,'李四','2023-7-5');
-- 修改表中数据update t_student set sex = '女' ;update t_student set sex = '男' where sno = 10 ;UPDATE T_STUDENT SET AGE = 21 WHERE SNO = 10;update t_student set CLASSNAME = 'java01' where sno = 10 ;update t_student set CLASSNAME = 'JAVA01' where sno = 9 ;update t_student set age = 29 where classname = 'java01';-- 删除操作：delete from t_student where sno = 2;
