在SQL中使用GROUP BY时，有一些事必须注意：

在SQL中使用GROUP BY时，有一些事必须注意：

1。不能使用别名
2。除了函数字段，SELECT出现的所有字段都必须在GROUP BY中出现
3。别名不要使用保留字

不同的数据库要求不一样，MYSQL没有这些限制，SQL SERVER有1，2的限制，ORACLE有1，2，3的限制。

比如以下几个都不对：
select count(*), to_char(TS,'YYYYMMDD') as date, protocol_name from TRANSACTIONS where PROTOCOL_NAME = 'cXML' group by date, PROTOCOL_NAME order by date

select count(*), to_char(TS,'YYYYMMDD') as date, protocol_name from TRANSACTIONS where PROTOCOL_NAME = 'cXML' group by to_char(TS,'YYYYMMDD') order by date

select count(*), to_char(TS,'YYYYMMDD') as date, protocol_name from TRANSACTIONS where PROTOCOL_NAME = 'cXML' group by to_char(TS,'YYYYMMDD'), PROTOCOL_NAME order by date

这个才对：
select count(*), to_char(TS,'YYYYMMDD') as t_date, protocol_name from TRANSACTIONS where PROTOCOL_NAME = 'cXML' group by to_char(TS,'YYYYMMDD'), PROTOCOL_NAME order by t_date