mysqlgroupby语句实现原理（Mysql中错误使用SQL语句Groupby被兼容的情况）

create table stud(
sno varchar(30) not null primary key,
sname varchar(30) not null,
age int,
saddress varchar(30)
);
INSERT INTO stud VALUES('1001','Tom',22,'湖南益阳');
INSERT INTO stud VALUES('1002','Jack',23,'益阳');
INSERT INTO stud VALUES('1003','李白',22,'益阳');
INSERT INTO stud VALUES('1004','王五',24,'中国北京');
INSERT INTO stud VALUES('1005','张三',22,'益阳');
INSERT INTO stud VALUES('1006','张四',23,'益阳');
INSERT INTO stud VALUES('1007','李四',22,'湖南益阳');
INSERT INTO stud VALUES('1008','刘备',24,'北京');

<喎�"/kf/ware/vc/" target="_blank" class="keylink">vcD4NCjxwcmUgY2xhc3M9"brush:sql;"> SELECT * FROM stud GROUP BY saddress;

ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'hncu.stud.sno' which is not functionally dependent
on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SELECT saddress as 平均年龄 FROM stud GROUP BY saddress;

SELECT * FROM stud GROUP BY saddress;

select a,b,c from table_name group by a,b,c,d;
select a,b from table_name group by a,b,c;
select a,max(a) from table_name group by a,b,c;

select a,b,c from table_name group by a,b;
select a,b,c from table_name group by a;