Nested Case Statement Logic

Question

I am working on a query to flatten some wp_postsmeta data in a WordPress database and need to set a specific value on various meta_values. I have a key of category and various category values, for each value, I want to set a column named color with a named color for our brand palette

    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 has many values, Marketing, HR, Company Holiday, etc, and for each subcategory I want each row to have a specific color.

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

Is the best way to achieve this to use a nested CASE WHEN against the meta_value? Or is there a better way?

I also tried including an if statement (below) but that duplicated each row.

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

Yes, the nested CASE statement would be the right way to go if you know all the categories and colors beforehand. If the category-colors are in another table, you can do either a subselect or a JOIN instead.

Here's an example with nested case:

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)