topn_array
description
Syntax
ARRAY<T> topn_array(expr, INT top_num[, INT space_expand_rate])
该topn_array函数使用Space-Saving算法计算expr中的top_num个频繁项，结果为频繁项及其出现次数，该结果为近似值
space_expand_rate参数是可选项，该值用来设置Space-Saving算法中使用的counter个数
counter numbers = top_num * space_expand_ratespace_expand_rate的值越大，结果越准确，默认值为50
example
mysql> select topn_array(k3,3) from baseall;
+--------------------------+
| topn_array(`k3`, 3) |
+--------------------------+
| [3021, 2147483647, 5014] |
+--------------------------+
1 row in set (0.02 sec)
mysql> select topn_array(k3,3,100) from baseall;
+--------------------------+
| topn_array(`k3`, 3, 100) |
+--------------------------+
| [3021, 2147483647, 5014] |
+--------------------------+
1 row in set (0.02 sec)keywords
TOPN, TOPN_ARRAY