Question

My current code

SELECT post_id, ( 3959 * ACOS( COS( RADIANS( 34.09 ) ) * COS( RADIANS( lat ) ) * COS( RADIANS( lng ) - RADIANS( -117.55 ) ) + SIN( RADIANS( 34.09 ) ) * SIN( RADIANS( lat ) ) ) ) AS distance FROM wp_postmeta WHERE `meta_key` LIKE '%location_l%' HAVING distance < 2500 ORDER BY distance LIMIT 0 , 20

Here are two sample row of data (meta_key is not always long or lat):

post_id = 123  
meta_key = location_longitude  
meta_value = -119.890000  

post_id = 123  
meta_key = location_latitude   
meta_value = 42.170000

How do I modify my query to replace ‘lat’ and ‘lng’ in my original query to be the contents of the meta_value listed above? Something like this?

select meta_value where meta_key = location_latitude

Answer 1

If you GROUP BY post_id, you should be able to use MAX() aggregates in place of lat,lng, surrounding CASE statements which determine whether the current row is latitude or longitude. The others will be NULL, and therefore eliminated by the aggregate.

I think this ought to work so you won’t need any subselects.

SELECT
   post_id, 
   ( 3959 * ACOS( COS( RADIANS( 34.09 ) ) * COS( RADIANS( MAX(CASE WHEN meta_key='location_latitude' THEN meta_value ELSE NULL END) ) ) * COS( RADIANS( MAX(CASE WHEN meta_key='location_longitude' THEN meta_value ELSE NULL END) ) - RADIANS( -117.55 ) ) + SIN( RADIANS( 34.09 ) ) * SIN( RADIANS( MAX(CASE WHEN meta_key='location_latitude' THEN meta_value ELSE NULL END) ) ) ) ) AS distance 
FROM wp_postmeta 
WHERE `meta_key` IN ('location_latitude','location_longitude')
GROUP BY post_id
HAVING distance < 2500 
ORDER BY distance 
LIMIT 0 , 20

The moving parts here are:

MAX(CASE WHEN meta_key='location_latitude' THEN meta_value ELSE NULL END)

This translates as: If this row’s meta_key is 'location_latitude', return the meta_value, otherwise return NULL. We expect then that since two rows are returned for the post_id (lat,lng), the MAX() value returned above is always the non-null one — the correct latitude or longitude value from meta_value.