几个简单常用的Sql语句

select SUM(Gnumber) as Ids from Goods where Cids = '';
--查Cids为2的Gnumber列的和，列名为Ids
select Cids,Plevel from People;
select * from Salary;
select * from Salary,People where People.Plevel = Salary.Slevel;
--查Salary,People两个表
select SUM(Ssalary) as salary from Salary,People where People.Plevel = Salary.Slevel and Cids = '';
--合并Salary,People，查Cids为2的Ssalary列的和，列名为salary