Creating a combined view of two spatially indexed tables

Question

Hi All,
I'm using oracle 10g and C++ occi to store and retrieve data. I have two tables that are identical in structure, they have an SDO_GEOM column where I store lat/long/altitude info. When I store the data using a stored procedure, the data is put into the correct table. I now want to retrieve the data using a spatial operator - I use SDO_NN to retrive data within a given distance of a lat/long/altitude point. This works fine for a single or multiple tables as I use a stored function to give me the data back as an object. I now have a requirement to list all the data from both tables - I thought I could do this by creating a combined view but I understand this cannot be done with spatial data - I habe also tried using the join operator but I am having problems since the columns for each table are identical. Is there any workaround for this - the combined view will not have any spatial operators run on it, I just need to return each row (the spatial data can be returned as individual lat/long/alt instead of as a SDO_GEOM. A second idea I had would be to return all the data using a ref cursor - this works for a single table but I do not understand how I can open the cursor with a select from two tables with identical column names.
Unfortunately it is a requirement that the tables are seperate so combining the two tables into one is not an option.
Thanks in advance for any help anyone can offer,
Cheers,
Rob

Answer 1

You can create a UNION ALL view:
CREATE TABLE cola_markets_1 (
mkt_id NUMBER PRIMARY KEY,
name VARCHAR2(32),
shape SDO_GEOMETRY);
CREATE TABLE cola_markets_2 (
mkt_id NUMBER PRIMARY KEY,
name VARCHAR2(32),
shape SDO_GEOMETRY);
CREATE VIEW v1 AS
SELECT * FROM cola_markets_1 UNION ALL SELECT * FROM cola_markets_2;
If both tables have a spatial index on their shape column, a query plan will look
like:
explain plan for SELECT c.mkt_id, c.name FROM v1 c WHERE SDO_NN(c.shape, SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1,1003,3), SDO_ORDINATE_ARRAY(4,6, 8,8)) , 'sdo_num_res=1') = 'TRUE';
0 SELECT STATEMENT     |           |
1 VIEW               | V1          |
2 UNION-ALL          |           |
3 TABLE ACCESS BY INDEX ROWID| COLA_MARKETS_1
4 DOMAIN INDEX     | COLA_SPATIAL_IDX_1
5 TABLE ACCESS BY INDEX ROWID| COLA_MARKETS_2
6 DOMAIN INDEX     | COLA_SPATIAL_IDX_2
However, the above SDO_NN query will return 2 rows (one from each table),
because it can only work on one table, it won't return the nearest neighbor
from the combined view without some tweaks. For example, to return the
top one, you may try:
select * from (SELECT c.mkt_id, c.name FROM v1 c WHERE SDO_NN(c.shape, SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1,1003,3), SDO_ORDINATE_ARRAY(4,6, 8,8)) , 'sdo_num_res=1') = 'TRUE' order by sdo_geom.sdo_distance(c.shape, SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1,1003,3), SDO_ORDINATE_ARRAY(4,6, 8,8)), 0.0001)) where rownum < 2;
Note that you can only pass literals or bind variables into the second input parameter
of spatial operators (including SDO_NN), when a UNION ALL view is used. i.e. the following
query won't work right now:
SELECT c.* FROM v1 c, another_table b WHERE b.id =1 and SDO_NN(c.shape, b.shape, 'sdo_num_res=1')= 'TRUE';