ST_SymDifference(g1, g2)

Returns a geometry that represents the point set symmetric difference
of the geometry values g1 and g2, which is defined as:

g1 symdifference g2 := (g1 union g2) difference (g1 intersection g2)

Or, in function call notation:

ST_SymDifference(g1, g2) = ST_Difference(ST_Union(g1, g2), ST_Intersection(g1, g2))

The result is in the same SRS as the geometry arguments.

ST_SymDifference() permits arguments in either a Cartesian or a
geographic SRS, and handles its arguments as described in the
introduction to this section.

URL: https://dev.mysql.com/doc/refman/8.4/en/spatial-operator-functions.html

