sql - Mysql - 改进 'group by'中的咨询查询

Question

我有一个“分组依据”的查询:

SELECT date_audience, 
    Sum( If( quality_apuration = '1', 1, 0 ) ) AS very_good, 
    Sum( If( quality_apuration = '2', 1, 0 ) ) AS good, 
    Sum( If( quality_apuration = '3', 1, 0 ) ) AS bad, 
    Sum( If( quality_apuration = '4', 1, 0 ) ) AS no_apuration, 
    Count(quality_apuration) AS total 

    FROM pp_base 

    WHERE date_audience >= '2011-01-01' AND date_audience <= '2011-02-28'

    GROUP BY date_audience ORDER BY date_audience ASC

在哪里返回以下结果(或参见 http://jsbin.com/imuru5/ ):

由于表X有另一个表Y的外键，最终有人会要求在表Y中添加一个项目，例如:'exccelent'，'regular'等。我也必须调整计划为 php $query[0]['very_good']、$query[0]['good']、$query[0]['bad'] 等，添加其他项目，花费更多时间。

有谁知道我该如何改进这个查询，以便自动生成结果？

谢谢，维尼修斯。

Answer 1

我可以看到两个选项。

1)在应用中处理。以下查询将在数据库中执行必要的聚合，并为每个 date_audience 返回 4 行(每个 quality_apuration 值一个)。

select date_audience
      ,quality_apuration
      ,count(*)
  from pp_base
 where date_audience >= date '2011-01-01' 
   and date_audience <= date '2011-02-28'
 group 
    by date_audience
      ,quality_apuration
 order
    by date_audience
      ,quality_apuration;

当您希望更改 quality_apuration 值时，这是首选。

2) 在数据库中处理。您可以定义如下 View :

create or replace view pp_view as
   select date_audience
         ,sum(case when quality_apuration = '1' then 1 else 0 end) as very_good
         ,sum(case when quality_apuration = '2' then 1 else 0 end) as good
         ,sum(case when quality_apuration = '3' then 1 else 0 end) as bad
         ,sum(case when quality_apuration = '4' then 1 else 0 end) as no_apuration
         ,count(quality_apuration) as total
     from pp_base 
    group 
       by date_audience;

...然后您将从应用程序中选择如下:

select ...
  from pp_view
 where date_audience >= date '2011-01-01' 
   and date_audience <= date '2011-02-28'
 order 
    by date_audience;

当然，无论何时为 quality_apuration 添加另一个值，都必须修改 View 定义。不过，这总比修改所有查询要好。