ST_Envelope(g)

ST_StartPoint(ls)

ST_EndPoint(ls)

ST_PointN(ls, N)

ST_ExteriorRing(poly)

ST_InteriorRingN(poly, N)

ST_GeometryN(gc, N)

Buffer(g, d [, strategy1 [, strategy2 [, strategy3]]])

ST_Buffer() and Buffer() are synonyms. For more information, see the description of ST_Buffer().

Buffer() is deprecated; expect it to be removed in a future MySQL release. Use ST_Buffer() instead.

ConvexHull(g)

ST_ConvexHull() and ConvexHull() are synonyms. For more information, see the description of ST_ConvexHull().

ConvexHull() is deprecated; expect it to be removed in a future MySQL release. Use ST_ConvexHull() instead.

ST_Buffer(g, d [, strategy1 [, strategy2 [, strategy3]]])

Returns a geometry that represents all points whose distance from the geometry value g is less than or equal to a distance of d, or NULL if any argument is NULL. The SRID of the geometry argument must be 0 because ST_Buffer() supports only the Cartesian coordinate system. If any geometry argument is not a syntactically well-formed geometry, an ER_GIS_INVALID_DATA error occurs.

If the geometry argument is empty, ST_Buffer() returns an empty geometry.

If the distance is 0, ST_Buffer() returns the geometry argument unchanged:

mysql> SET @pt = ST_GeomFromText('POINT(0 0)');
mysql> SELECT ST_AsText(ST_Buffer(@pt, 0));
+------------------------------+
| ST_AsText(ST_Buffer(@pt, 0)) |
+------------------------------+
| POINT(0 0)                   |
+------------------------------+

ST_Buffer() supports negative distances for Polygon and MultiPolygon values, and for geometry collections containing Polygon or MultiPolygon values. The result may be an empty geometry. An ER_WRONG_ARGUMENTS error occurs for ST_Buffer() with a negative distance for Point, MultiPoint, LineString, and MultiLineString values, and for geometry collections not containing any Polygon or MultiPolygon values.

ST_Buffer() permits up to three optional strategy arguments following the distance argument. Strategies influence buffer computation. These arguments are byte string values produced by the ST_Buffer_Strategy() function, to be used for point, join, and end strategies:

Up to one strategy of each type may be specified, and they may be given in any order. If multiple strategies of a given type are specified, an ER_WRONG_ARGUMENTS error occurs.

mysql> SET @pt = ST_GeomFromText('POINT(0 0)');
mysql> SET @pt_strategy = ST_Buffer_Strategy('point_square');
mysql> SELECT ST_AsText(ST_Buffer(@pt, 2, @pt_strategy));
+--------------------------------------------+
| ST_AsText(ST_Buffer(@pt, 2, @pt_strategy)) |
+--------------------------------------------+
| POLYGON((-2 -2,2 -2,2 2,-2 2,-2 -2))       |
+--------------------------------------------+

mysql> SET @ls = ST_GeomFromText('LINESTRING(0 0,0 5,5 5)');
mysql> SET @end_strategy = ST_Buffer_Strategy('end_flat');
mysql> SET @join_strategy = ST_Buffer_Strategy('join_round', 10);
mysql> SELECT ST_AsText(ST_Buffer(@ls, 5, @end_strategy, @join_strategy))
+---------------------------------------------------------------+
| ST_AsText(ST_Buffer(@ls, 5, @end_strategy, @join_strategy))   |
+---------------------------------------------------------------+
| POLYGON((5 5,5 10,0 10,-3.5355339059327373 8.535533905932738, |
| -5 5,-5 0,0 0,5 0,5 5))                                       |
+---------------------------------------------------------------+

ST_Buffer() and Buffer() are synonyms.

ST_Buffer_Strategy(strategy [, points_per_circle])

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

Information about strategies is available at Boost.org.

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

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. 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().

ST_ConvexHull(g)

Returns a geometry that represents the convex hull of the geometry value g. If the argument is NULL, the return value is NULL.

This function computes a geometry's convex hull by first checking whether its vertex points are colinear. The function returns a linear hull if so, a polygon hull otherwise. This function processes geometry collections by extracting all vertex points of all components of the collection, creating a MultiPoint value from them, and computing its convex hull. If the argument is an empty geometry collection, the return value is NULL.

mysql> SET @g = 'MULTIPOINT(5 0,25 0,15 10,15 25)';
mysql> SELECT ST_AsText(ST_ConvexHull(ST_GeomFromText(@g)));
+-----------------------------------------------+
| ST_AsText(ST_ConvexHull(ST_GeomFromText(@g))) |
+-----------------------------------------------+
| POLYGON((5 0,25 0,15 25,5 0))                 |
+-----------------------------------------------+

ST_ConvexHull() and ConvexHull() are synonyms.

ST_Difference(g1, g2)

Returns a geometry that represents the point set difference of the geometry values g1 and g2. If any argument is NULL, the return value is NULL.

mysql> SET @g1 = Point(1,1), @g2 = Point(2,2);
mysql> SELECT ST_AsText(ST_Difference(@g1, @g2));
+------------------------------------+
| ST_AsText(ST_Difference(@g1, @g2)) |
+------------------------------------+
| POINT(1 1)                         |
+------------------------------------+

ST_Intersection(g1, g2)

Returns a geometry that represents the point set intersection of the geometry values g1 and g2. If any argument is NULL, the return value is NULL.

mysql> SET @g1 = ST_GeomFromText('LineString(1 1, 3 3)');
mysql> SET @g2 = ST_GeomFromText('LineString(1 3, 3 1)');
mysql> SELECT ST_AsText(ST_Intersection(@g1, @g2));
+--------------------------------------+
| ST_AsText(ST_Intersection(@g1, @g2)) |
+--------------------------------------+
| POINT(2 2)                           |
+--------------------------------------+

ST_SymDifference(g1, g2)

Returns a geometry that represents the point set symmetric difference of the geometry values g1 and g2, which is defined as:

g1 symdifference g2 := (g1 union g2) difference (g1 intersection g2)

Or, in function call notation:

ST_SymDifference(g1, g2) = ST_Difference(ST_Union(g1, g2), ST_Intersection(g1, g2))

If any argument is NULL, the return value is NULL.

mysql> SET @g1 = ST_GeomFromText('MULTIPOINT(5 0,15 10,15 25)');
mysql> SET @g2 = ST_GeomFromText('MULTIPOINT(1 1,15 10,15 25)');
mysql> SELECT ST_AsText(ST_SymDifference(@g1, @g2));
+---------------------------------------+
| ST_AsText(ST_SymDifference(@g1, @g2)) |
+---------------------------------------+
| MULTIPOINT((1 1),(5 0))               |
+---------------------------------------+

ST_Union(g1, g2)

Returns a geometry that represents the point set union of the geometry values g1 and g2. If any argument is NULL, the return value is NULL.

mysql> SET @g1 = ST_GeomFromText('LineString(1 1, 3 3)');
mysql> SET @g2 = ST_GeomFromText('LineString(1 3, 3 1)');
mysql> SELECT ST_AsText(ST_Union(@g1, @g2));
+--------------------------------------+
| ST_AsText(ST_Union(@g1, @g2))        |
+--------------------------------------+
| MULTILINESTRING((1 1,3 3),(1 3,3 1)) |
+--------------------------------------+