识别 Null 空间对象

可使用 Vertica IS NULL 和 IS NOT NULL 结构来识别 null GEOMETRY 和 GEOGRAPHY 对象。

以下示例使用下面的表，其中 id=2 的行在 geog 字段中包含 null 值。

=> SELECT id, ST_AsText(geom), ST_AsText(geog) FROM locations
   ORDER BY 1 ASC;
 id |           ST_AsText              |                 ST_AsText
----+----------------------------------+--------------------------------------
  1 | POINT (2 3)                      | POINT (-85 15)
  2 | POINT (4 5)                      |
  3 | POLYGON ((-1 2, 0 3, 1 2, -1 2)) | POLYGON ((-24 12, -15 23, -20 27, -24 12))
  4 | LINESTRING (-1 2, 1 5)           | LINESTRING (-42.74 23.98, -62.19 23.78)
(4 rows)

识别具有 null geog 值的所有行：

=> SELECT id, ST_AsText(geom), (ST_AsText(geog) IS NULL) FROM locations
   ORDER BY 1 ASC;
 id |            ST_AsText             | ?column?
----+----------------------------------+----------
  1 | POINT (2 3)                      | f
  2 | POINT (4 5)                      | t
  3 | POLYGON ((-1 2, 0 3, 1 2, -1 2)) | f
  4 | LINESTRING (-1 2, 1 5)           | f
(4 rows)

识别 geog 值不为 null 的行：

=> SELECT id, ST_AsText(geom), (ST_AsText(geog) IS NOT NULL) FROM locations
   ORDER BY 1 ASC;
 id |            st_astext             | ?column?
----+----------------------------------+----------
  1 | POINT (2 3)                      | t
  2 | POINT (4 5)                      | f
  3 | LINESTRING (-1 2, 1 5)           | t
  4 | POLYGON ((-1 2, 0 3, 1 2, -1 2)) | t
(4 rows)