Question

我有两个ActiveRecord查询。一个返回4，这是正确的数字，另一个返回11，这是错误的计数。我希望两个查询都返回4.即使在Rails控制台中呈现的SQL对于两个AR查询都是相同的。

首先查询：

campaign.daily_statistics.select('COUNT(DISTINCT user_id) AS count').where(metric: metric).where("properties -> '#{column}' = '#{value}'")[0]['count']
DailyStatistic Load (0.7ms)  SELECT COUNT(DISTINCT user_id) AS count FROM "daily_statistics" WHERE "daily_statistics"."campaign_id" = $1 AND "daily_statistics"."metric" = 'participation' AND (properties -> 'assumed_gender' = 'female')  [["campaign_id", 2]]
=> 4

第二次查询：

sql = campaign.daily_statistics.select('COUNT(DISTINCT user_id) AS count')
sql.where(metric: metric).where("properties -> '#{column}' = '#{value}'")
sql[0]['count']
DailyStatistic Load (0.9ms)  SELECT COUNT(DISTINCT user_id) AS count FROM "daily_statistics" WHERE "daily_statistics"."campaign_id" = $1 AND "daily_statistics"."metric" = 'participation' AND (properties -> 'assumed_gender' = 'female')  [["campaign_id", 2]]
=> 11

有人能解释一下这里发生了什么吗？

Answer 1

在您的第二个查询中，您未分配

sql.where(metric: metric).where("properties -> '#{column}' = '#{value}'")

任何事情。所以当你运行

时

sql[0]['count']

您只执行分配给sql变量的查询的第一部分。

我不确定为什么SQL日志记录输出会像它一样出现。据猜测，由于rails控制台的某些特性以及提供输出/内联日志记录的原因。

Answer 2

您应该在rails控制台中看到的内容如下：

sql = campaign.daily_statistics.select('COUNT(DISTINCT user_id) AS count')
DailyStatistic Load (0.9ms)  SELECT COUNT(DISTINCT user_id) AS count FROM "daily_statistics" WHERE "daily_statistics"."campaign_id" = $1)  [["campaign_id", 2]]
sql.where(metric: metric).where("properties -> '#{column}' = '#{value}'")
DailyStatistic Load (0.9ms)  SELECT COUNT(DISTINCT user_id) AS count FROM "daily_statistics" WHERE "daily_statistics"."campaign_id" = $1 AND "daily_statistics"."metric" = 'participation' AND (properties -> 'assumed_gender' = 'female')  [["campaign_id", 2]]
sql[0]['count']
#=> 11

第二个查询的修复应该是：

sql = campaign.daily_statistics.select('COUNT(DISTINCT user_id) AS count')
DailyStatistic Load (0.9ms)  SELECT COUNT(DISTINCT user_id) AS count FROM "daily_statistics" WHERE "daily_statistics"."campaign_id" = $1)  [["campaign_id", 2]]
sql2 = sql.where(metric: metric).where("properties -> '#{column}' = '#{value}'")
DailyStatistic Load (0.9ms)  SELECT COUNT(DISTINCT user_id) AS count FROM "daily_statistics" WHERE "daily_statistics"."campaign_id" = $1 AND "daily_statistics"."metric" = 'participation' AND (properties -> 'assumed_gender' = 'female')  [["campaign_id", 2]]
sql2[0]['count']
#=> 4

为什么相同的SQL查询会返回不同的结果？

2 个答案: