jiayuasu commented on code in PR #621:
URL: https://github.com/apache/incubator-sedona/pull/621#discussion_r857045727
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sql/src/main/scala/org/apache/spark/sql/sedona_sql/expressions/Functions.scala:
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@@ -1620,6 +1620,47 @@ case class ST_Reverse(inputExpressions: Seq[Expression])
}
/**
+ * Returns the nth point in the geometry, provided it is a linestring
+ *
+ * @param inputExpressions sequence of 2 input arguments, a geometry and a
value 'n'
+ */
+case class ST_PointN(inputExpressions: Seq[Expression])
+ extends Expression with CodegenFallback {
+ inputExpressions.validateLength(2)
+
+ override def nullable: Boolean = true
+
+ lazy val GeometryFactory = new GeometryFactory()
+ lazy val emptyGeometry: GeometryCollection =
GeometryFactory.createGeometryCollection(null)
Review Comment:
This emptyGeometry is NOT consistent with PostGIS requirement. ST_PointN
should return NULL if no input linestring. You return an empty
GeometryCollection but not NULL. https://postgis.net/docs/ST_PointN.html
Please fix this and add corresponding test cases for non-line string input.
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