PERCENTILE_APPROX

description

Syntax

PERCENTILE_APPROX(expr, DOUBLE p[, DOUBLE compression])

返回第p个百分位点的近似值,p的值介于0到1之间

compression参数是可选项,可设置范围是[2048, 10000],值越大,精度越高,内存消耗越大,计算耗时越长。 compression参数未指定或设置的值在[2048, 10000]范围外,以10000的默认值运行

该函数使用固定大小的内存,因此对于高基数的列可以使用更少的内存,可用于计算tp99等统计值

example

MySQL > select `table`, percentile_approx(cost_time,0.99)
from log_statis
group by `table`;
+----------+--------------------------------------+
| table    | percentile_approx(`cost_time`, 0.99) |
+----------+--------------------------------------+
| test     |                                54.22 |
+----------+--------------------------------------+

MySQL > select `table`, percentile_approx(cost_time,0.99, 4096)
from log_statis
group by `table`;
+----------+----------------------------------------------+
| table    | percentile_approx(`cost_time`, 0.99, 4096.0) |
+----------+----------------------------------------------+
| test     |                                        54.21 |
+----------+----------------------------------------------+

keyword

PERCENTILE_APPROX,PERCENTILE,APPROX