Oracle Spatial User's Guide and Reference - InfoLab

Querying Spatial Data
evaluated against the PARKS table. Thus, the SDO_WITHIN_DISTANCE operation
is performed n times if there are n rows in the COASTLINES table.
For non-geodetic data, there is an efficient way to accomplish a spatial join that
involves buffering all geometries of a layer. This method does not use the SDO_
WITHIN_DISTANCE operator. First, create a new table COSINE_BUFS as follows:
CREATE TABLE cosine_bufs UNRECOVERABLE AS
SELECT SDO_BUFFER (A.SHAPE, B.DIMINFO, 1.35)
FROM COSINE A, USER_SDO_GEOM_METADATA B
WHERE TABLE_NAME='COSINES' AND COLUMN_NAME='SHAPE';
Next, create a spatial index on the SHAPE column of COSINE_BUFS. Then you can
perform the following query:
SELECT a.gid, b.gid FROM parks a, cosine_bufs b,
TABLE(SDO_JOIN('PARKS', 'SHAPE', 'COSINE_BUFS', 'SHAPE',
'mask=ANYINTERACT')) c
WHERE c.rowid1 = a.rowid AND c.rowid2 = b.rowid;
4.2.1.4 Nearest Neighbor Operator
The SDO_NN operator, described in Chapter 12, is used to identify the nearest
neighbors for a geometry. This operator can be used only if a spatial index has been
created on two dimensions of data. The syntax of the operator is as follows:
SDO_NN(geometry1 SDO_GEOMETRY,
geometry2 SDO_GEOMETRY,
param VARCHAR2
[, number NUMBER]);
In the preceding syntax:
■ geometry1 is a column of type SDO_GEOMETRY in a table. This column must
be spatially indexed.
■ geometry2 is an instance of type SDO_GEOMETRY.
■ param is a quoted string of a keyword value pair that determines how many
nearest neighbor geometries are returned by the operator. See the SDO_NN
operator in Chapter 12 for information about this parameter.
■ number is the same number used in the call to SDO_NN_DISTANCE. Use this
only if the SDO_NN_DISTANCE ancillary operator is included in the call to
SDO_NN. See the SDO_NN operator in Chapter 12 for information about this
parameter.
Indexing and Querying Spatial Data 4-15