ST_IsSimple(g)

Returns 1 if the geometry value g has no anomalous geometric points,
such as self-intersection or self-tangency. ST_IsSimple() returns 0 if
the argument is not simple, and NULL if the argument is NULL.

The descriptions of the instantiable geometric classes given under
https://dev.mysql.com/doc/refman/5.7/en/opengis-geometry-model.html
includes the specific conditions that cause class instances to be
classified as not simple.

URL: https://dev.mysql.com/doc/refman/5.7/en/gis-general-property-functions.html

