1d9b3aeee7
The error format '##keyword' in a lot of docs. This pr is to repair document format. #4335
2.1 KiB
Executable File
2.1 KiB
Executable File
title, language
| title | language |
|---|---|
| PERCENTILE_APPROX | zh-CN |
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