Given two shapes A and B, ST_Equals(A, B) returns true if every point in the set of points that make up A is also in B, and if every point in the set of points that make up B is also in A. The ordering of the points in A and B may differ, but they must be made up of equivalent sets.
Another way of describing ST_Equals(A, B) is that it will return true if both ST_Within(A, B) and ST_Within(B, A) also return true.
ST_Equals works on the following data types:
ST_Equals will attempt to use any available spatial index to speed up its operation. Use the prefixed variant _ST_Equals if you do not want any spatial indexes to be used.
Examples
The screenshots in these examples were generated using geojson.io, but they are designed to showcase the shapes, not the map. Representing GEOMETRY data in GeoJSON can lead to unexpected results if using geometries with SRIDs other than 4326 (as shown below).
True
In this example, ST_Equals returns true because:
- Every Point in the set of Points that make up Polygon A is also in Polygon B, and every Point in the set of Points that make up Polygon B is also in Polygon A
As mentioned above, the ordering of the points in A and B does not matter. Below, there are two triangles with the same vertices, which are ordered differently. In the screenshot, one triangle is drawn in yellow, and the other blue. The blue and yellow strokes of the two separate triangles' boundaries are visible. Because the images are overlaid on each other, the yellow and blue combine to make part of the exterior outline of the image a green color.
SELECT st_equals(st_geomfromtext('SRID=4326;POLYGON((-87.906471 43.038902, -95.992775 36.153980, -75.704722 36.076944, -87.906471 43.038902))'), st_geomfromtext('SRID=4326;POLYGON((-95.992775 36.153980, -87.906471 43.038902, -75.704722 36.076944, -95.992775 36.153980))'));
st_equals
---------------
true
(1 row)
False
In this example, ST_Equals returns false because:
- It's obvious that not every Point that makes up the set of Points in Polygon A is not also in Polygon B.
SELECT st_equals(st_geomfromtext('SRID=4326;POLYGON((-87.906471 43.038902, -95.992775 36.153980, -75.704722 36.076944, -87.906471 43.038902))'), st_geomfromtext('SRID=4326;POLYGON((-84.191605 39.758949, -75.165222 39.952583, -78.878738 42.880230, -84.191605 39.758949))'));
st_equals
---------------
false
(1 row)
See also
- Working with Spatial Data
- Spatial and GIS Glossary of Terms
- Spatial indexes
- Spatial functions
ST_CoversST_CoveredByST_ContainsST_WithinST_IntersectsST_CoveredByST_CoversST_DisjointST_OverlapsST_TouchesST_ConvexHullST_Union- Migrate from Shapefiles
- Migrate from GeoJSON
- Migrate from GeoPackage
- Migrate from OpenStreetMap
- Introducing Distributed Spatial Data in Free, Open Source CockroachDB (blog post)
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