Overlay Functions

ST_Union

Dual parameter variant

Description: Unions the input geometries, merging geometry to produce a result geometry with no overlaps
Input Argument #1: Geometry (WKB)
Input Argument #2: Geometry (WKB)
Output: The spatial union of the two input geometries (WKB)

SELECT ST_AsText(
  ST_Union(
    ST_GeomFromText(
      'POINT(1 2)'
    ), 
    ST_GeomFromText(
      'POINT(-2 3)'
    )
  )
)

Result

MULTIPOINT ((-2 3), (1 2))

Aggregating variant

ST_Difference

Description: Returns a geometry representing the part of geometry #1 that does not intersect with geometry #2
Input Argument #1: Geometry (WKB)
Input Argument #2: Geometry (WKB)
Output: The spatial (non-symmetric) difference between the 2 input geometries (WKB)

SELECT ST_AsText(
  ST_Difference(
    ST_GeomFromText(
      'LINESTRING(50 100, 50 200)'
    ),
    ST_GeomFromText(
      'LINESTRING(50 50, 50 150)'
    )
  )
)

Result

LINESTRING (50 150, 50 200)

ST_Intersection

Description: Returns a point-set geometry representing the part of geometry #1 that intersects with geometry #2
Input Argument #1: Geometry (WKB)
Input Argument #2: Geometry (WKB)
Output: The spatial intersection between the 2 input geometries (WKB)

SELECT ST_AsText(
  ST_Intersection(
    ST_GeomFromText(
      'POLYGON((1 2,1 5,4 5,4 2,1 2))'
    ), 
    ST_GeomFromText(
      'POLYGON((3 1,3 3,5 3,5 1,3 1))'
    )
  )
)

Result

POLYGON ((4 3, 4 2, 3 2, 3 3, 4 3))