Can I make this SQL query more efficient?

Question

I have an SQL query which works fine, but I feel like there must be a more efficient way of writing it. By joining two tables A and B that contain coordinates, I am comparing distances (in metres) between each coordinate. I then sum/count the number of coordinates in table B that are within set distances of coordinates in table A and output the result:

select a.name,
       sum(case when ST_GeodesicLengthWGS84(ST_SetSRID(ST_LineString(a.lat, a.lon, b.lat, b.lon),4326)) < 10.0 then 1 else 0 end) 10mCount,
       sum(case when ST_GeodesicLengthWGS84(ST_SetSRID(ST_LineString(a.lat, a.lon, b.lat, b.lon),4326)) < 50.0 then 1 else 0 end) 50mCount,
       sum(case when ST_GeodesicLengthWGS84(ST_SetSRID(ST_LineString(a.lat, a.lon, b.lat, b.lon),4326)) < 1000.0 then 1 else 0 end) 1000mCount 
FROM a JOIN
     b
GROUP BY a.name
ORDER by 1000mCount desc
LIMIT 10;

I feel like there must be a way to call ST_GeodesicLengthWGS84(ST_SetSRID(ST_LineString(a.lat, a.lon, b.lat, b.lon), 4326)) once, get the result and then increment each 10m, 50m and 1000m count.

Any ideas? Thanks.

Answer 1

Try prequerying, but your data is STILL requiring the results to go through EVERY RECORD.

select
      PreQuery.name,
      sum(case when PreQuery.Geode < 10.0 then 1 else 0 end) 10mCount,
      sum(case when PreQuery.Geode < 50.0 then 1 else 0 end) 50mCount,
      sum(case when PreQuery.Geode < 1000.0 then 1 else 0 end) 1000mCount 
   from
      ( select 
              a.name,
              ST_GeodesicLengthWGS84( ST_SetSRID( ST_LineString(a.lat, a.lon, b.lat, b.lon),4326)) as Geode
           from 
              a join b  
                 (YOU ARE MISSING the JOIN 'ON' clause... how related) ) PreQuery
   GROUP BY 
      PreQuery.name
   ORDER by 
      1000mCount desc
   LIMIT 10;