涉及内部联接和分组依据的SQL查询

Question

I need help with a MySQL query that will optimize my Rails 3 application.

I have 2 tables: segments and custom properties.

Table defs are:

segments
- name
- organization_id
- ancestry
- ancestry_depth

custom_properties
- name
- label
- value
- segment_id

Segments are tree-like structures, thus the ancestry columns. eg Segment 3 is a child of Segment 2 is a child of Segment 1. Each of those segments will have the same custom properties, however, the values could come from an inherited segment (a segment up the tree) instead of from the segment itself. If a value of a particular property is inherited from a segment up the tree, then its value is set to null.

My goal is to retrieve custom properties for a particular segment, in a single SQL statement, while taking into consideration the depth of the segment since depth determines the priority order of the values that I need.

The current query I have is very close, it returns the correct number of properties for a particular segment, however, with that group by statement I always get the property with the lowest ID, but what I really need is the property with the highest depth. If I take out the group by then I get duplicate properties, 1 from each segment listed in the "IN". But again, I only need property from the highest depth.

SELECT custom_properties.name, 
       custom_properties.value, 
       segments.ancestry_depth 
FROM   custom_properties 
       INNER JOIN segments 
         ON custom_properties.object_id = segments.id 
WHERE  custom_properties.object_type = 'Segment' 
       AND custom_properties.object_id IN ( 86770, 86637, 40667, 180 ) 
       AND custom_properties.value IS NOT NULL 
GROUP  BY custom_properties.name 
ORDER  BY custom_properties.name, 
          segments.ancestry_depth DESC 

I hope this makes sense. I appreciate any help and/or direction.

Thank you!

Louis

Answer 1

Try removing the DESC keyword from the ORDER BY clause.

EDIT:

Try the following:

SELECT v.*
FROM   (SELECT custom_properties.name, 
               custom_properties.value, 
               segments.ancestry_depth 
        FROM   custom_properties 
               INNER JOIN segments 
                 ON custom_properties.object_id = segments.id 
        WHERE  custom_properties.object_type = 'Segment' 
               AND custom_properties.object_id IN ( 86770, 86637, 40667, 180 ) 
               AND custom_properties.value IS NOT NULL 
        ORDER  BY custom_properties.name, 
                  segments.ancestry_depth DESC) v
GROUP  BY name 

Answer 2

Maby this wil work:

SELECT c.name, c.VALUE, s1.ancestry_depth, s2.ancestry_depth as depth
FROM custom_properties as c
JOIN segments s1 ON c.object_id = s1.id
LEFT JOIN segments s2 ON c.object_id = s2.id AND s2.ancestry_depth > s1.ancestry_depth
WHERE  c.object_type = 'Segment' 
AND c.object_id IN ( 86770, 86637, 40667, 180 ) 
AND c.VALUE IS NOT NULL 
GROUP  BY c.name 
HAVING ISNULL(depth)
ORDER  BY c.name, s1.ancestry_depth DESC 

edit: I misunderstood you and was selecting properties with biggest depth but i should select segnents with biggest depth