Using SCORE on top of View with UNION

Question

Hi guys,
I explain what I'm trying to do quickly:
2 Tables: table1 and table2 with same structure and both have a multi_column_datastore ctxsys.context.
1 View: view1
select * from table1
union
select * from table2
if I run:
select * from view1 WHERE contains(view1.COLUMN1,'%textext%',1 ) > 0;
this works fine, I get the correct result.
If I try to use SCORE function I have an error:
select * from view1 WHERE contains(view1.COLUMN1,'%textext%',1 ) > 0 ORDER by SCORE(1);
ORA-29921: Ancillary operator not supported with set view query block
I understand the problem is in the UNION inside the view,is there any way to make it works keep filtering the VIEW?
Thanks in advance

Answer 1

There is no score in the view, so you can't reference the score when querying the view.  In order to put the score in the view, you need a contains clause, which requires a value.  One method of doing this is to use sys_context.  Please see the reproduction of the problem and solution below.
SCOTT@orcl12c> -- reproduction of problem:
SCOTT@orcl12c> create table table1
  2    (column1  varchar2(30))
  3  /
Table created.
SCOTT@orcl12c> insert into table1 values ('textext')
  2  /
1 row created.
SCOTT@orcl12c> create table table2
  2    (column1 varchar2(30))
  3  /
Table created.
SCOTT@orcl12c> insert into table2 values ('textext')
  2  /
1 row created.
SCOTT@orcl12c> begin
  2    ctx_ddl.create_preference ('test_ds', 'multi_column_datastore');
  3    ctx_ddl.set_attribute ('test_ds', 'columns', 'column1');
  4  end;
  5  /
PL/SQL procedure successfully completed.
SCOTT@orcl12c> create index table1_idx on table1 (column1)
  2  indextype is ctxsys.context
  3  parameters ('datastore  test_ds')
  4  /
Index created.
SCOTT@orcl12c> create index table2_idx on table2 (column1)
  2  indextype is ctxsys.context
  3  parameters ('datastore  test_ds')
  4  /
Index created.
SCOTT@orcl12c> create or replace view view1
  2  as
  3  select * from table1
  4  union
  5  select * from table2
  6  /
View created.
SCOTT@orcl12c> select * from view1 where contains (view1.column1, '%textext%', 1) > 0
  2  /
COLUMN1
textext
1 row selected.
SCOTT@orcl12c> select * from view1 where contains (view1.column1,'%textext%',1 ) > 0 order by score(1)
  2  /
select * from view1 where contains (view1.column1,'%textext%',1 ) > 0 order by score(1)
ERROR at line 1:
ORA-29921: Ancillary operator not supported with set view query block
SCOTT@orcl12c> -- solution:
SCOTT@orcl12c> create or replace view view1
  2  as
  3  select score(1) score, table1.* from table1
  4  where  contains (table1.column1, sys_context ('text_query', 'query_value'), 1) > 0
  5  union
  6  select score(1) score, table2.* from table2
  7  where  contains (table2.column1, sys_context ('text_query', 'query_value'), 1) > 0
  8  /
View created.
SCOTT@orcl12c> create or replace context text_query using text_proc
  2  /
Context created.
SCOTT@orcl12c> create or replace procedure text_proc
  2    (p_val in varchar2)
  3  as
  4  begin
  5    dbms_session.set_context ('text_query', 'query_value', p_val);
  6  end text_proc;
  7  /
Procedure created.
SCOTT@orcl12c> exec text_proc ('%textext%')
PL/SQL procedure successfully completed.
SCOTT@orcl12c> set autotrace on explain
SCOTT@orcl12c> select * from view1 order  by score
  2  /
     SCORE COLUMN1
         3 textext
1 row selected.
Execution Plan
Plan hash value: 4090246122
| Id  | Operation                       | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT                |            |     2 |    60 |     8   (0)| 00:00:01 |
|   1 |  SORT ORDER BY                  |            |     2 |    60 |     8   (0)| 00:00:01 |
|   2 |   VIEW                          | VIEW1      |     2 |    60 |     8   (0)| 00:00:01 |
|   3 |    SORT UNIQUE                  |            |     2 |    58 |     8  (50)| 00:00:01 |
|   4 |     UNION-ALL                   |            |       |       |            |          |
|   5 |      TABLE ACCESS BY INDEX ROWID| TABLE1     |     1 |    29 |     4   (0)| 00:00:01 |
|*  6 |       DOMAIN INDEX              | TABLE1_IDX |       |       |     4   (0)| 00:00:01 |
|   7 |      TABLE ACCESS BY INDEX ROWID| TABLE2     |     1 |    29 |     4   (0)| 00:00:01 |
|*  8 |       DOMAIN INDEX              | TABLE2_IDX |       |       |     4   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   6 - access("CTXSYS"."CONTAINS"("TABLE1"."COLUMN1",SYS_CONTEXT('text_query','query_v
              alue'),1)>0)
   8 - access("CTXSYS"."CONTAINS"("TABLE2"."COLUMN1",SYS_CONTEXT('text_query','query_v
              alue'),1)>0)
Note
   - dynamic statistics used: dynamic sampling (level=2)
SCOTT@orcl12c>