聚合函数 count,max,min,avg,sum... select count (*) from T_Employee select Max(FSalary) from T_Employee 排序 ASC升序 DESC降序 select * from T_Employee order by Fage 先按年龄降序排列。如果年龄相同，则按薪水升序排
聚合函数 count,max,min,avg,sum... select count (*) from T_Employee select Max(FSalary) from T_Employee 排序 ASC升序 DESC降序 select * from T_Employee order by Fage 先按年龄降序排列。如果年龄相同，则按薪水升序排列 select * from T_Employee order by FAge DESC,FSalary ASC order by 要放在 where 子句之后 通配符过滤 通配符过滤用like 单字符通配符‘_' 多字符通配符‘%' select * from T_Employee where FName like '_erry' NULL 是不知道的意思，而不是没有 用SQL语句查询NULL的数据不能用=或<> 而用is NULL或者is not NULL select * from T_Employee where FName is NULL in(23,25)同时匹配两个值。相当于 23 or 25 between 20 and 30 匹配介于20到30之间的数 group by分组 select FAge, count(*) from T_Employee Group by Fage 先把相同的Fage分一组，再统计每一组的个数 group by子句要放在where子句之后。如果想取某个年龄段人数大于1的，不能用where count（*） > 1 ，因为聚合函数不能放在where子句之后。要用having子句 Having是对分组后的列进行过滤，能用的列和select中的一样。如下例中则不能用having Fsalary>2000 只能用where Fsalary>2000 select FAge, count(*) from T_Employee Group by FAge having count(*) > 1; 限制结果集的范围 select Top 3 * from T_Employee order by FSalary DESC 从第六名开始选3个.2005后可以用Row_Number函数 select Top 3 * from T_Employee where FNumber not in(select TOP 5 FNumber from T_Employee order by FSalary DESC) order by FSalary DESC
