ST_Touches(g1, g2)

Two geometries spatially touch if their interiors do not intersect, but
the boundary of one of the geometries intersects either the boundary or
the interior of the other.

This function returns 1 or 0 to indicate whether g1 spatially touches
g2.

As of MySQL 5.7.5, this function returns 0 if called with an
inapplicable geometry argument type combination. For example, it
returns 0 if either of the arguments is a Point or MultiPoint.

URL: http://dev.mysql.com/doc/refman/5.7/en/spatial-relation-functions-object-shapes.html

