My question is about how
ST_Union of rasters containing NULL values are handled. For example suppose I have two rasters that intersect but the values of the intersection are NULL in one of the rasters. According to the documentation
ST_Union takes the last value by default.
Does this mean that the unionized raster would contain null values at the intersecting locations where the second raster was null? In other words if one of the two rasters contains null values at the intersecting points (pixels) does order matter?
I am motivated to understand this because some of my rasters were not perfectly aligned and
ST_SnapToGrid created extra an extra row/column on some of my rasters that contains only null values.