MBRCoveredBy(g1, g2)

Returns 1 or 0 to indicate whether the minimum bounding rectangle of g1
is covered by the minimum bounding rectangle of g2. This tests the
opposite relationship as MBRCovers().

MBRCoveredBy() handles its arguments as follows:

o If either argument is NULL or an empty geometry, the return value is
  NULL.

o If either argument is not a syntactically well-formed geometry byte
  string, an ER_GIS_INVALID_DATA error occurs.

o Otherwise, the return value is non-NULL.

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

