总结:1.插入数据:insert into b(a,l) values(1,"2");insert into b values();
2、修改数据:update b set name='',ir= where id= ; 3、删除数据:delete from b where id= ;truncate table b; delete from b; 4、查询数据:select * from b; 5.查询指定字段,多项目查询:select pdate,pname from b where id=1; 6.查询时增加常量:select id as '',pname as '' where id=1; 7.查询去重:select distinct sex from b ; 8.查询时计算:select pname,(a+s+f) from b where id= ; 9.条件查询:selelct name from b where product='新的'; 10.< > <> <= >=的使用:select js from socre where grade>50 or grade<80 or grade>=65 or grade<=75 or grade <> 66; 11.between and 的用法:select * from f where grade= between 60 and 70; 12.null和空字符串的用法:null是没有值具体用法:is null或者is not null;''空字符串是有 值但是值是空的,没有被实参赋值是空字符串。 12.%和_的用法:%表示一个或多个任意字符,_表示一个任意字符;一般和like模糊查询一起使用 查询姓张的人:select * from teacher where name like '张%'; 查询姓张名字是三个字的人:select * from teacher where name like '张__'; 13.SUM/AVG/MAX/MIN/COUNT()的用法: 求和:select sum(js) from scroe;求js成绩的总和 求js成绩的平均数;select avg(js) from scroe; 求css的最高成绩:select max(css) from scroe; 求css的最低成绩:select min(css) from scroe; 求学js的人数:select js,count(*) from scroe group by js; 14.ASC DESC的用法;ASC是正序从小到大;DESC是倒叙从大到小; css成绩从小到大进行排序;selelct * from scroe group by css asc; js成绩从大到小进行排序:select * from scroe group by js desc; group by 是分组计数;order by 是进行排序用的 SELECT * FROM score ORDER BY js ASC,jquery DESC;-- 是以js为主排序,当js的值相同的是 时候再按照jquery的成绩排; 15.有关count()方法的使用 查询每个班的人数:select clas,count(*)from student group by clas; 16.查询每个班js的总分:select clas,count(js) from student group by clas;