TOPN_WEIGHTED

description

Syntax

ARRAY<T> topn_weighted(expr, BigInt weight, INT top_num[, INT space_expand_rate])

该topn_weighted函数使用Space-Saving算法计算，取expr中权重和为前top_num个数组成的结果，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_weighted(k5,k1,3) from baseall;
2. +------------------------------+
3. | topn_weighted(`k5`, `k1`, 3) |
4. +------------------------------+
5. | [0, 243.325, 100.001]        |
6. +------------------------------+
7. 1 row in set (0.02 sec)

9. mysql> select topn_weighted(k5,k1,3,100) from baseall;
10. +-----------------------------------+
11. | topn_weighted(`k5`, `k1`, 3, 100) |
12. +-----------------------------------+
13. | [0, 243.325, 100.001]             |
14. +-----------------------------------+
15. 1 row in set (0.02 sec)

keywords

TOPN, TOPN_WEIGHTED