create table salary (userid int,salary decimal(9,2));

-- mysql
insert into salary values(1,1000),(2,2000), (3,3000),(4,4000),(5,5000), (1,null),(2,500);
-- oracle
　　insert all
　　　　into salary values(1,1000)
　　　　into salary values(2,2000)
　　　　into salary values(3,3000)
　　　　into salary values(4,4000)
　　　　into salary values(5,5000)
　　　　into salary values(1,null)
　　　　into salary values(2,500)
　　　　select * from dual;

-- if(value,t f)
　　select salary, if(salary>2000,‘high‘,‘low‘) hl from salary; -- oracke 不支持

-- case when ... then...else...end

　　select salary, case when salary<=2000 then ‘low‘ else ‘high‘ end hl from salary;
　　select salary, case when salary<=2000 then ‘low‘ when salary is null then ‘low‘ when salary<=4000 then

-- case ... when ... then...else...end
　　select salary, case salary when 1000 then ‘low‘ when 2000 then ‘mid‘ else ‘high‘ end hl from salary;

sql 流程函數