PostGIS raster - sum of rasters

Question

I have raster data stored in a PostgreSQL/PostGIS database. I need to create a summed raster from certain rasters.

Something like:

select sum(raw_data) as image from data where rid > 2 AND rid < 5; 

But this is not the correct function. What is?

Answer 1

Use ST_Union(rast, 'SUM')

Overlapping pixels will be summed into a new raster. Note there are also FIRST, MIN, MAX, COUNT, MEAN, RANGE options for the uniontype paramter.