to_char(sysdate,'yyyy-mm-dd hh:mi:ss') from dual
to_date
to_number
nvl(common,0) --将把空替换为0
nvl2(exp1,expr2,expr3) --expr==expr2?null:epxr1
case语句
select ename,job,sal,
case job when 'SALESMAN' then sal*0.9
when 'MANAGER' then sal*0.85
from salary
decode函数
select ename,job,sal,
decode(job,'SALESMAN',sal*0.9,
'MANAGER',sal*0.85
)as t_sal --别名
from semp