Question

我正在研究将WordPress数据库中的wp_postsmeta数据展平的查询，并且需要在各种meta_values上设置特定值。我有一个类别键和各种类别值，对于每个值，我想为我们的品牌调色板设置一个名为color的列，并为其命名一种颜色。

    select post_title as title, 
 MAX(CASE WHEN meta_key='corporate_calendar_category' THEN meta_value END) as 'category',
 MAX(CASE WHEN meta_key = 'corporate_calendar_subcategory' THEN meta_value END) as 'subcategory',

 // Do I need to include a nested CASE WHEN?
 MAX(CASE WHEN meta_key = 'corporate_calendar_subcategory' and meta_value = 'Marketing' THEN 'blueLagoon' END) as 'color',

 MAX(CASE WHEN meta_key = 'corporate_calendar_presenter' THEN meta_value END) as 'presenter',
 MAX(CASE WHEN meta_key = 'corporate_calendar_date' THEN meta_value END) as 'start_date',
 MAX(CASE WHEN meta_key = 'corporate_calendar_time' THEN meta_value END) as 'start_time',
 MAX(CASE WHEN meta_key = 'corporate_calendar_duration' THEN meta_value END) as 'duration',
 MAX(CASE WHEN meta_key = 'corporate_calendar_registration_link' THEN meta_value END) as 'registration_link',
 MAX(CASE WHEN meta_key = 'corporate_calendar_description' THEN meta_value END) as 'description',
 MAX(CASE WHEN meta_key = 'corporate_calendar_image_path' THEN meta_value END) as 'image_path'

FROM   wp_posts p 
JOIN wp_postmeta m ON p.id = m.post_id
where p.post_type = 'calendar-event'
and p.post_status = 'publish'
GROUP BY p.id

corporate_calendar_subcategory具有许多值，包括Marketing，HR，Company Holiday等，对于每个子类别，我希望每行具有特定的颜色。

title     category   subcategory       color        presenter   start_date etc.
Example   Training   Marketing         blueLagoon   someone     08/29/2018
Labor Day Reminder   Company Holiday   camelot                  09/03/2018
etc
etc

实现此目标的最佳方法是对meta_value使用嵌套的CASE吗？还是有更好的方法？

我还尝试在下面添加一个if语句，但是每行重复一次。

if(meta_key = 'corporate_calendar_subcategory', 
 CASE
   WHEN meta_value = 'Marketing' THEn 'blueLagoon'
   WHEN meta_value = 'Company Holiday' THEN 'camelot'
 END,
 '') as color,

Answer 1

是的，如果您事先知道所有类别和颜色，则嵌套CASE语句将是正确的方法。如果类别颜色在另一个表中，则可以执行子选择或JOIN。

这是一个嵌套案例的例子：

max(case when meta_key = 'corporate_calendar_subcategory' then
    case meta_value
        when 'Marketing' then 'blue'
        when 'Sales' then 'yellow
        when 'Development' then 'red'
    end
end)

嵌套案例陈述逻辑

1 个答案: