SQL 添加用户创建的结果行答案

【问题标题】：SQL Add a user created results rowSQL 添加用户创建的结果行
【发布时间】：2013-11-06 00:14:10
【问题描述】：

我有以下查询：

SELECT 
num.description,
(num.new_driver_form/denom.form_sent_to) as conversion
FROM
(SELECT
'Common' as description,
count(DISTINCT u1.user_id) as new_driver_form
FROM   
user_tags u1
JOIN   
user_tags u2 USING (user_id)
WHERE  
u1.name = 'sentForm'
AND    
u2.name = 'recForm')num
JOIN
(SELECT
'Common' as description,
count(DISTINCT user_id) as form_sent_to
FROM 
user_tags
WHERE
name = 'sentForm')denom
ON num.description = denom.description

我收到“未能找到从未知到文本的转换函数”的错误，但我不确定这是什么意思。

【问题讨论】：

描述来自哪里？

标签： sql postgresql

【解决方案1】：

您需要添加明确的type cast 以避免错误。 'Common' 只是一个字符串文字，Postgres 希望您提供它应该转换为的类型。

您还需要将 num.new_driver_form (count() returns bigint) 中的 bigint 数字转换为 numeric（或有损浮点类型），以便从您的除法中获得有意义的结果。然后您将对round() 函数感兴趣。

SELECT num.description
     ,(num.new_driver_form::numeric / denom.form_sent_to) AS conversion
FROM  (
   SELECT 'Common'::text AS description
         ,count(DISTINCT u1.user_id) AS new_driver_form
   FROM   user_tags u1
   JOIN   user_tags u2 USING (user_id)
   WHERE  u1.name = 'sentForm'
   AND    u2.name = 'recForm'
   ) num
JOIN   (
   SELECT 'Common'::text AS description
         ,count(DISTINCT user_id) AS form_sent_to
   FROM   user_tags
   WHERE  name = 'sentForm'
   ) denom ON num.description = denom.description

当然，您的JOIN 一开始并没有多大意义，因为第二个子查询计算单行并且JOIN 条件始终为TRUE。可以简化为：

SELECT num.description
     ,(num.new_driver_form::numeric / denom.form_sent_to) AS conversion
FROM  (
   SELECT 'Common'::text AS description
         ,count(DISTINCT u1.user_id) AS new_driver_form
   FROM   user_tags u1
   JOIN   user_tags u2 USING (user_id)
   WHERE  u1.name = 'sentForm'
   AND    u2.name = 'recForm'
   ) num
JOIN   (
   SELECT count(DISTINCT user_id) AS form_sent_to
   FROM   user_tags
   WHERE  name = 'sentForm'
   ) denom ON TRUE

或者只使用子查询：

SELECT 'Common'::text AS description
      ,(count(DISTINCT u1.user_id)::numeric
       / (SELECT count(DISTINCT user_id)
          FROM   user_tags
          WHERE  name = 'sentForm')) AS conversion
FROM   user_tags u1
JOIN   user_tags u2 USING (user_id)
WHERE  u1.name = 'sentForm'
AND    u2.name = 'recForm'

【讨论】：

【解决方案2】：

这个方法很简单

SELECT
  'cohort' as description,
  count(DISTINCT u1.user_id) as new_driver_form,
  x.field as field
FROM user_tags u1
JOIN user_tags u2 USING (user_id)
JOIN anothertable X ON x.blah = u1.blah
WHERE  
  u1.name = 'sentForm'
  AND    
  u2.name = 'recForm'

如果字符串来自其中一个表，这样的事情会起作用：

SELECT
  <replace with field name> as description,
  count(DISTINCT u1.user_id) as new_driver_form,
  x.field as field
FROM user_tags u1
JOIN user_tags u2 USING (user_id)
JOIN anothertable X ON x.blah = u1.blah
WHERE  
  u1.name = 'sentForm'
  AND    
  u2.name = 'recForm'

【讨论】：

我知道这是一个后续问题，但我这样做并尝试加入另一个查询，我也添加了“队列”作为描述。这不可能吗？
我在两个表中都创建了“描述”，错误是“找不到从未知到文本的转换函数”
@Stuave - 你必须发布 sql，我不知道为什么会出现这个错误