MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

12.16.7 Geometry Property Functions

Each function that belongs to this group takes a geometry value as its argument and returns some quantitative or qualitative property of the geometry. Some functions restrict their argument type. Such functions return NULL if the argument is of an incorrect geometry type. For example, the ST_Area() polygon function returns NULL if the object type is neither Polygon nor MultiPolygon.