Postgis calculate the distance between points

Question

I have a table that has more than 15k rows.

The table has locationID, isEmpty, longitude and latitude fields.

I want to calculate the distance between each point has isEmpty field = 1 and the others and insert the result into new table using Postgis.

Please advise what is the best practice for writing sql statement executing this requirement

Answer 1

Ok, thanks for explanations - now it's clearer.

In Postgis you don't have to count all distances to find how many other points are within some distance.

1. Add extension to database

    CREATE EXTENSION postgis; 

2. Now add a column of type geometry

    ALTER TABLE mytable ADD COLUMN geom geometry; 

3. You'll need some index to

    CREATE INDEX mytable_geom_idx ON mytable USING gist(geom); 

4. Now populate new column

    UPDATE mytable SET geom = ST_SetSRID(ST_MakePoint(lon, lat),4326); 

5. And now the query:

    Select a.locationID, count(*) from mytable a join mytable b on a.locationID!=b.locationID and ST_Dwithin(a.geom::geography,b.geom::geography,152) where a.isEmpty=1 group by 1; 

ST_DWithin with geography type is taking distance in meters and 152m~500ft

I didn't test it, so if something will not work please write me a comment