- 类别：
ST_BUFFER¶
返回一个表示 MultiPolygon 的 GEOMETRY 对象，其中包含输入 GEOMETRY 对象指定距离内的点。返回的对象有效表示输入对象周围的一个“缓冲区”。
您还可以通过指定负的距离值来“缩小”输入对象。
语法¶
ST_BUFFER( <geometry_expression> , <distance> )
实参¶
geometry_expression实参必须是 GEOMETRY 类型的表达式。
distance与 GEOMETRY 对象的距离。要“缩小”对象，可以指定负的距离值。
该单位取决于 GEOMETRY 对象的 空间参考系统标识符 (SRID) (link removed)。例如，ESPG:4326 (https://epsg.io/4326) 单位是度，而 ESPG:25855 (https://epsg.io/25833) 单位是米。
返回¶
返回一个 GEOMETRY 对象。
使用说明¶
SRIDs 基于 EPSG 标准 (https://epsg.org/home.html) (v10.082)。例如，SRID 4326 对应于代码为 4326 的机构 EPSG。
ST_BUFFER 使用八个段来模拟四分之一圆。
如果
distance为负值，则返回的对象小于输入对象。可以利用这一点来消除形状中微小的不规则性。对于 LineStrings，端盖和联接样式始终是圆形。
LineStings 始终在两侧缓冲。
示例¶
在执行示例之前，将 GEOMETRY_OUTPUT_FORMAT 参数设置为 WKT：
ALTER SESSION SET GEOMETRY_OUTPUT_FORMAT='WKT';
以下示例返回一个围绕着点且半径为 1 的多边形：
SELECT ST_BUFFER(TO_GEOMETRY('POINT(0 0)'), 1) AS geom;
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| GEOM |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| MULTIPOLYGON(((1 0,0.9807852804 -0.195090322,0.9238795325 -0.3826834324,0.8314696123 -0.555570233,0.7071067812 -0.7071067812,0.555570233 -0.8314696123,0.3826834324 -0.9238795325,0.195090322 -0.9807852804,6.123233996e-17 -1,-0.195090322 -0.9807852804,-0.3826834324 -0.9238795325,-0.555570233 -0.8314696123,-0.7071067812 -0.7071067812,-0.8314696123 -0.555570233,-0.9238795325 -0.3826834324,-0.9807852804 -0.195090322,-1 7.657137398e-16,-0.9807852804 0.195090322,-0.9238795325 0.3826834324,-0.8314696123 0.555570233,-0.7071067812 0.7071067812,-0.555570233 0.8314696123,-0.3826834324 0.9238795325,-0.195090322 0.9807852804,2.480838239e-15 1,0.195090322 0.9807852804,0.3826834324 0.9238795325,0.555570233 0.8314696123,0.7071067812 0.7071067812,0.8314696123 0.555570233,0.9238795325 0.3826834324,0.9807852804 0.195090322,1 0))) |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
以下示例使用负的 distance 值从形状中消除微小的不规则性（如尖峰）。TO_GEOMETRY 调用将 TRUE 作为第二个实参传入，从而允许函数为 无效的形状 创建一个 GEOMETRY 对象。
SELECT ST_BUFFER(TO_GEOMETRY('SRID=2261;POLYGON((
1540792.21541900 290472.63529214, 1547018.61770388 302537.02285369,
1546965.96550151 302752.51514772, 1547018.61770388 302537.02285369,
1549532.42729914 301257.07398027, 1543327.42218339 289322.60923536,
1540792.21541900 290472.63529214))', True), -1e-08) AS geom;
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| GEOM |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| MULTIPOLYGON(((1543327.42218339 289322.609235373,1540792.21541901 290472.635292145,1547018.61770388 302537.022853677,1549532.42729913 301257.073980266,1543327.42218339 289322.609235373))) |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+