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，返回由前top_num个组成的数组，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

1. counter numbers = top_num * space_expand_rate

space_expand_rate的值越大，结果越准确，默认值为50

example

1. mysql> select topn_array(k3,3) from baseall;
2. +--------------------------+
3. | topn_array(`k3`, 3)      |
4. +--------------------------+
5. | [3021, 2147483647, 5014] |
6. +--------------------------+
7. 1 row in set (0.02 sec)

9. mysql> select topn_array(k3,3,100) from baseall;
10. +--------------------------+
11. | topn_array(`k3`, 3, 100) |
12. +--------------------------+
13. | [3021, 2147483647, 5014] |
14. +--------------------------+
15. 1 row in set (0.02 sec)

keywords

TOPN, TOPN_ARRAY