ST_Buffer_Strategy(strategy[,points_per_circle])

This function returns a strategy byte string for use with ST_Buffer()
to influence buffer computation. The result is NULL if any argument is
NULL. If any argument is invalid, an ER_WRONG_ARGUMENTS error occurs.

Information about strategies is available at Boost.org
(http://www.boost.org).

The first argument must be a string indicating a strategy option:

o For point strategies, permitted values are 'point_circle' and
  'point_square'.

o For join strategies, permitted values are 'join_round' and
  'join_miter'.

o For end strategies, permitted values are 'end_round' and 'end_flat'.

If the first argument is 'point_circle', 'join_round', 'join_miter', or
'end_round', the points_per_circle argument must be given as a positive
numeric value. The maximum points_per_circle value is the value of the
max_points_in_geometry system variable as of MySQL 5.7.8, 65,536 before
that. If the first argument is 'point_square' or 'end_flat', the
points_per_circle argument must not be given or an ER_WRONG_ARGUMENTS
error occurs.

For examples, see the description of ST_Buffer().

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

