聚合函數 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
先按年齡降序排列。如果年齡相同，則按薪水升序排列 select * from T_Employee order by FAge DESC,FSalary ASC
order by 要放在 where 子句之后
通配符過濾 通配符過濾用like 單字符通配符‘_' 多字符通配符‘%' select * from T_Employee where FName like '_erry'
NULL 是不知道的意思，而不是沒有 用SQL語句查詢NULL的數據不能用=或> 而用is NULL或者is not NULL select * from T_Employee where FName is NULL
in(23,25)同時匹配兩個值。相當于 23 or 25
between 20 and 30 匹配介于20到30之間的數
group by分組 select FAge, count(*) from T_Employee Group by Fage 先把相同的Fage分一組，再統計每一組的個數
group by子句要放在where子句之后。如果想取某個年齡段人數大于1的，不能用where count（*） > 1 ，因為聚合函數不能放在where子句之后。要用having子句 Having是對分組后的列進行過濾，能用的列和select中的一樣。如下例中則不能用having Fsalary>2000 只能用where Fsalary>2000 select FAge, count(*) from T_Employee Group by FAge having count(*) > 1;
限制結果集的范圍 select Top 3 * from T_Employee order by FSalary DESC
從第六名開始選3個.2005后可以用Row_Number函數 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
