ST_BUFFER 純量函數
ST_BUFFER 函數會採用幾何佈置物件及距離 (以公尺為單位) 作為輸入參數，並傳回新的結果幾何佈置，其中結果幾何佈置界限上的每一個點都是與指定幾何佈置的指定距離。
結果幾何形狀的邊界中的任何圓形曲線都以線性字串近似。 例如，點周圍的緩衝區會產生圓形區域，以其界限為線串的多邊形近似。 近似圓中要使用的預設多邊形邊數為 8。
如果 geometry 是空值，則結果是空值。 無法緩衝空的幾何佈置。 如果 geometry 是空的，則會傳回錯誤。
- 幾何佈置
- St_Geometry 類型的值，或代表用來建立緩衝區之幾何佈置的其中一個子類型。
- 距離
- 倍精準度浮點數值，指定用於 幾何佈置周圍緩衝區的距離。 此距離以公尺為測量單位。
函數的結果為 ST_GEOMETRY。
範例
將 10 公里的緩衝區套用至各種幾何佈置。
CREATE TABLE sample_geometries(id INTEGER, geometry QSYS2.ST_GEOMETRY);
INSERT INTO sample_geometries VALUES
(1, QSYS2.ST_POINT('point(50 50)')),
(2, QSYS2.ST_LINESTRING('linestring(20 10, 21 13, 22 14)')),
(3, QSYS2.ST_POLYGON('polygon((-10 -12, -11 -14, -13 -14, -13 -12, -10 -12))'));
SELECT id, QSYS2.ST_GEOMETRYTYPE(geometry) AS spatial_text, QSYS2.ST_ASTEXT(QSYS2.ST_BUFFER(geometry, 10000)) AS buffer_10k
FROM sample_geometries;結果：
ID SPATIAL_TEXT BUFFER_10K
---- --------------- --------------------------------------------------------------------
1 ST_POINT POLYGON ((49.942004 50.089817,
49.860139 50.037124999999996,
49.860355 49.962706999999995,
49.94222 49.910154,
50.05778 49.910154,
50.139644999999994 49.962706999999995,
50.139860999999996 50.037124999999996,
50.057995999999996 50.089817,
49.942004 50.089817))
2 ST_LINESTRING POLYGON ((20.924315999999997 13.063383,
20.919014 13.047649,
20.907192 13.035749,
20.907564 13.013665,
19.913235999999998 10.027735999999999,
19.901574999999998 9.992343,
19.935903 9.926048,
20.007758 9.903068,
20.075072 9.936854,
20.086748999999998 9.972241,
21.080956 12.952326999999999,
22.066225 13.937234,
22.093018999999998 13.963849,
22.092132 14.038262999999999,
22.037253999999997 14.090266999999999,
21.960532 14.089376999999999,
21.933739 14.062748,
20.944551 13.07335,
20.924315999999997 13.063383))
3 ST_POLYGON POLYGON ((-9.946252999999999 -11.925657,
-9.962472 -11.909965,
-9.979156 -11.910055,
-9.994169 -11.902935,
-10.015716 -11.91025,
-12.961767 -11.910366999999999,
-12.961972 -11.910166,
-12.999749999999999 -11.910167999999999,
-13.037528 -11.909965,
-13.037735999999999 -11.910166,
-13.038027999999999 -11.910166,
-13.064748 -11.936299,
-13.091617 -11.962287,
-13.091619 -11.962572999999999,
-13.091826 -11.962776,
-13.091838 -11.99974,
-13.092056999999999 -12.036705,
-13.091852 -12.036907,
-13.092582 -13.999794,
-13.092758 -14.036812,
-13.092595999999999 -14.03697,
-13.092597 -14.037192,
-13.065621 -14.063378,
-13.038753999999999 -14.089671,
-13.038525 -14.089671,
-13.038364 -14.089827999999999,
-13.000197 -14.089832,
-11.021272 -14.089919,
-11.006274999999999 -14.097042,
-10.984385 -14.089768,
-10.961246 -14.089671,
-10.949489999999999 -14.078166999999999,
-10.933695 -14.072913999999999,
-10.923525999999999 -14.052754,
-10.907242 -14.036812,
-10.907319 -14.020617,
-9.923986 -12.052576,
-9.907943 -12.036705,
-9.90804 -12.02038,
-9.900763999999999 -12.005688,
-9.908251 -11.984605,
-9.908382999999999 -11.962287,
-9.92025 -11.950809999999999,
-9.925723999999999 -11.935388999999999,
-9.946252999999999 -11.925657))