mysql加权随机结果 - 如何在SELECT之后获取变量值

Question

我有一个表keywords，其中包含keyword列和weight列。我的目标是随机选择一个keyword，但要考虑其weight（概率）。我找到了两种方法来解决这个问题，后一种方法更优雅（并且消耗更少的资源） - 但我不能让它运行。看看你自己。

表和记录：

CREATE TABLE IF NOT EXISTS `keywords` (
  `keyword` varchar(100) COLLATE utf8_bin NOT NULL,
  `weight` int(11) NOT NULL,
  UNIQUE KEY `keywords` (`keyword`),
  KEY `rate` (`weight`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

INSERT INTO `keywords` (`keyword`, `weight`) VALUES
('google', 50),
('microsoft', 20),
('apple', 10),
('yahoo', 5),
('bing', 5),
('xing', 5),
('cool', 5);

查询1

消耗更多的资源，我处理5k +记录。来源是Why would this MySQL query using rand() return no results about a third of the time?：

SELECT *  FROM `keywords` ORDER BY -LOG(1.0 - RAND()) / weight LIMIT 1

查询2

将权重汇总到@weight_sum。从该范围内将@weight_point设置为RAND()个数字。循环浏览所有记录，从weight中减去@weight_pos并将@keyword设置为当前keywords.keyword。直到@weight_pos < 0。然后它保留keyword。来源是Random Weighted Choice in T-SQL

SET @keyword = 0;
SET @weight_sum = (SELECT SUM(weight) FROM keywords);
SET @rand = RAND();
SET @weight_point = ROUND(((@weight_sum - 1) * @rand + 1), 0);
SET @weight_pos = @weight_point;

SELECT
    keyword,
    weight,

    @keyword:=CASE
        WHEN @weight_pos < 0 THEN @keyword
        ELSE keyword
    END AS test,

    (@weight_pos:=(@weight_pos - weight)) AS curr_weight,
    @weight_point,
    @keyword,
    @weight_pos,
    @rand,
    @weight_sum
FROM
    keywords;

请在此处查看phpmyadmin结果http://postimg.org/image/stgpd776f/

我的问题

如何获取@keyword中的值，或者test列最终保留的内容？之后添加SELECT @keyword不会改变任何内容。

Answer 1

好吧，我认为我的问题或多或少是一个基本的mysql问题。我通过将上面的SELECT语句封装到另一个SELECT中来实现我想要的，然后根据我搜索的内容过滤第一个SELECT的结果。对不起，打扰你。请参阅查询：

SET @keyword = 0;
SET @weight_sum = (SELECT SUM(weight) FROM keywords);
SET @rand = RAND();
SET @weight_point = ROUND(((@weight_sum - 1) * @rand + 1), 0);
SET @weight_pos = @weight_point;
SELECT t.test FROM (
SELECT
    keyword,
    weight,
    @keyword:=CASE
        WHEN @weight_pos < 0 THEN @keyword
        ELSE keyword
    END AS test,
    (@weight_pos:=(@weight_pos - weight)) AS curr_weight,
    @weight_point,
    #@keyword,
    @weight_pos,
    @rand,
    @weight_sum
FROM
    keywords

) AS t

WHERE
    t.curr_weight < 0
LIMIT
    1;