SQL中的函数——Trunc()

trunc(exp1)

trunc(exp1)和Round(exp1,exp2)类似，只不过trunc()不指定截取的小数位数进行处理，只取到整数位,不做舍去处理

select trunc(123.1234) from dual ---123
select trunc(123.9234) from dual ---123

-----Round(exp1,exp2)函数具有四舍五入的功能，分为以下两种情况

---exp2数为非负,四舍五入的位数从小数点后开始计数,小数点后|exp2|位,看後一位，进本位，后面舍去

select Round(125.455,0) from dual   ---125
select Round(125.455,1) from dual   ---125.5
select Round(125.455,4) from dual   ---125.455  大于小数位数，其余的位数补0将不显示



---exp2数为负,四舍五入的位数从小数点前开始计数,小数点前|exp2|位，看本位，进前一位，本位以及后面取0

select Round(125.455,-1) from dual   ---130
select Round(125.455,-2) from dual   ---100
select Round(125.455,-3) from dual   ---0
select Round(125.455,-4) from dual   ---0