centos7：mysql数据库（基本SQL语句---记录操作）

记录操作:
    增
        # 添加记录
            insert into 表明 set 字段=值; #(值是字符时需要加"")
                eg. insert into t1 set id=1,name='xiaoming';
            insert into 表名 values(值1,值2,....); #顺序按照表头的顺序（字符需要加引号）
                eg. insert into t2 values(2,'male','zhao',88);
                        insert into t2 (id,name,linux) values(3,'qian',90);
                        insert into t2 (id,name,linux) values(4,'sun',93),(5,'li',76);

    删
        # 删除记录,一定要有定位
            delete from t1 where name='haha';
        # 删除没有值的记录，即null
            delete from t1 where name is null;
            delete from t1 where name<=>null;
        # 清空表
            delete from t2;

    改
        # 修改记录,一定要有定位
            update 表名 set 修改字段=值 where 条件字段=值;
            eg. update t1 set sex='female' where id=3;

    查
        # 查看所有的记录
            select * from tb_name;
        # 查看指定字段的记录
            select id,name from t1;
        # 子查询
            select name,english from t1 where english=(select max(english) from t1);
        # 分组统计
            select sex,count(sex) from t2 group by sex;
        # 只显示前2条记录
            select name,chi from t2 order by chi desc limit 2;

    聚合函数
        sum() # 求和
            # 求指定字段的和
                select sum(linux) from t2;
            # 求指定字段的平均数
                select avg(linux) from t2;
            # 求和,并且给和设置字段名
                select name,chinese+math+english as total from t1;

    排序：
        # 升序：按照指定字段从小到大的顺序排列
            select name,linux from t2 order by linux;
        # 降序：按照指定字段从大到小的顺序排列，显示前3名
            select name,linux from t2 order by linux desc limit 3;

    通配符
        # % 匹配任意
            select * from t2 where name like '%an';
        # _ 匹配单个字符le
            select * from t2 where name like 'q_an';

    正则表达式：regexp
        # 匹配正则表达式
            select * from t2 where name regexp 'an$';

    运算符：
        # 多条件定位（and <---> && or <---> || != =）
            update t1 set sex='male' where id=1 and name='huang';
        # 多条件匹配 &&<=>and ||<=>or

            delete from t1 where id=1 && name='zhao';