TOPN_ARRAY

description

Syntax

ARRAY<T> topn_array(expr, INT top_num[, INT space_expand_rate])

The topn function uses the Space-Saving algorithm to calculate the top_num frequent items in expr, and return an array about the top n nums, which is an approximation

The space_expand_rate parameter is optional and is used to set the number of counters used in the Space-Saving algorithm

1. counter numbers = top_num * space_expand_rate

The higher value of space_expand_rate, the more accurate result will be. The default value is 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