DOUBLE|round(DOUBLE a)|Returns the rounded BIGINT value of a.返回对a四舍五入的BIGINT值
DOUBLE|round(DOUBLE a, INT d)|Returns a rounded to d decimal places.返回DOUBLE型d的保留n位小数的DOUBLW型的近似值
DOUBLE|bround(DOUBLE a)|Returns the rounded BIGINT value of a using HALF_EVEN rounding mode (as of Hive 1.3.0, 2.0.0). Also known as Gaussian rounding or bankers' rounding. Example: bround(2.5) = 2, bround(3.5) = 4.银行家舍入法（1~4：舍，6~9：进，5->前位数是偶：舍，5->前位数是奇：进）
DOUBLE|bround(DOUBLE a, INT d)|Returns a rounded to d decimal places using HALF_EVEN rounding mode (as of Hive 1.3.0, 2.0.0). Example: bround(8.25, 1) = 8.2, bround(8.35, 1) = 8.4.银行家舍入法,保留d位小数
BIGINT|floor(DOUBLE a)|Returns the maximum BIGINT value that is equal to or less than a向下取整，最数轴上最接近要求的值的左边的值 如：6.10->6 -3.4->-4
BIGINT|ceil(DOUBLE a), ceiling(DOUBLE a)|Returns the minimum BIGINT value that is equal to or greater than a.求其不小于小给定实数的最小整数如：ceil(6) = ceil(6.1)= ceil(6.9) = 6
DOUBLE|rand(), rand(INT seed)|Returns a random number (th来源：oschina
链接：https://my.oschina.net/u/4390903/blog/4540913