1.求绝对值 ，正值，负值：
ABS(numeric_type a)
POSITIVE(numeric_type a)
NEGATIVE(numeric_type a)
NEGATIVE 等同于 -abs(a)
POSITIVE 等同于 abs()
2.求余数，求商：
QUOTIENT(BIGINT numerator, BIGINT denominator), QUOTIENT(DOUBLE numerator, DOUBLE denominator)
FMOD(DOUBLE a, DOUBLE b), FMOD(FLOAT a, FLOAT b)
MOD(numeric_type a, same_type b)
PMOD(BIGINT a, BIGINT b), PMOD(DOUBLE a, DOUBLE b)
3.取浮点数的精度和小数点位数：
SCALE(numeric_expression)
PRECISION(numeric_expression)
4.阶乘运算
FACTORIAL(integer_type a)
阶乘函数和！符合效果一样
5.向上和向下取数
CEIL(DOUBLE a), CEIL(DECIMAL(p,s) a), CEILING(DOUBLE a), CEILING(DECIMAL(p,s) a), DCEIL(DOUBLE a), DCEIL(DECIMAL(p,s) a)
FLOOR(DOUBLE a), FLOOR(DECIMAL(p,s) a), DFLOOR(DOUBLE a), DFLOOR(DECIMAL(p,s) a)
6.常量函数pi和e
E
PI
7.求n次方 和求开方
POW(DOUBLE a, double p), POWER(DOUBLE a, DOUBLE p), DPOW(DOUBLE a, DOUBLE p), FPOW(DOUBLE a, DOUBLE p)
SQRT(DOUBLE a), DSQRT(DOUBLE a)
8.进制转换：
BIN(BIGINT a)
HEX(BIGINT a), HEX(STRING a)
UNHEX(STRING a)
CONV(BIGINT n, INT from_base, INT to_base), CONV(STRING s, INT from_base, INT to_base)
9.去最大值和最小值
GREATEST,LEAST
10.判断是否为无穷和NAN
IS_INF(DOUBLE a)
IS_NAN(DOUBLE a)
11.伪随机数：
RAND(), RAND(BIGINT seed), RANDOM(), RANDOM(BIGINT seed)
12. 分桶函数：Postgresql 9.6+ 和Oracle都支持的函数。
WIDTH_BUCKET(DECIMAL expr, DECIMAL min_value, DECIMAL max_value, INT num_buckets)
13.近视数取数：
TRUNCATE, DTRUNC, TRUNC
ROUND, DROUND
支持的数据类型：
ROUND(DOUBLE a), ROUND(DOUBLE a, INT d), ROUND(DECIMAL a, int_type d), DROUND(DOUBLE a), DROUND(DOUBLE a, INT d), DROUND(DECIMAL(p,s) a, int_type d)
TRUNCATE(DOUBLE_or_DECIMAL a[, digits_to_leave]), DTRUNC(DOUBLE_or_DECIMAL a[, digits_to_leave]), TRUNC(DOUBLE_or_DECIMAL a[, digits_to_leave])
14.HASH 函数：
FNV_HASH(type v)
MURMUR_HASH(type v)
15.LOG函数
16.正弦和余弦函数：
DEGREES(DOUBLE a)
RADIANS(DOUBLE a)
ACOS
ASIN
ATAN
ATAN2
COS
COSH
COT
SIGN
SIN
SINH
TAN
TANH
参考：
