Unexpected result of multiset mapping in Oracle SQL - sql

Question

Please help me to confirm is that behavior explained below is a bug, or clearly explain why it's right.
There are a high probability that I misunderstood some concept, but now for me it looks like a bug.
All examples below simplified as much as possible to demonstrate core of the issue. Real situation is very complex, so only general answers and workarounds related to principle of query construction is acceptable.
You are welcome to ask clarifying questions in comments and i'll try to do my best to answer them.
Thank you for attention. :)
Question
Why in last Example (Example 5) collection instance in (select count(1) ... subquery from first row mapped to all rows of the table, while expected result is to map each collection instance to it's own row?
At the same time collections used in cardinality(...) expression chosen properly.
Same situation (not covered in examples) exists if constructed in this way collections used in from or where part of a query.
Test schema setup
(SQLFiddle)
create or replace type TabType0 as table of varchar2(100)
/
create table Table0( tab_str_field varchar2(100), tab_field TabType0)
nested table tab_field store as tab_field_table
/
insert into table0 (tab_str_field, tab_field) values (
'A',
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual
) as TabType0)
)
/
insert into table0 (tab_str_field, tab_field) values (
'B',
cast(multiset(
select 'B' from dual union all
select 'C' from dual
) as TabType0)
)
/
insert into table0 (tab_str_field, tab_field) values (
'C',
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual union all
select 'D' from dual
) as TabType0)
)
/
insert into table0 (tab_str_field, tab_field) values (
'D',
cast(multiset(
select 'A' from dual
) as TabType0)
)
/
select 'Initial table data' caption from dual
/
select * from table0
/
table data:
| TAB_STR_FIELD | TAB_FIELD |
-----------------------------
| A | A,B,C |
| B | B,C |
| C | A,B,C,D |
| D | A |
Examples
Example 1 (SQLFiddle) - work with nested table fields - OK
select 'Work with nested table - OK' caption from dual
/
select
tab_field tab_field,
-- cardinality
cardinality(tab_field) tab_cardinality,
-- select from table field of current row
(select count(1) from table(tab_field)) tab_count,
-- select from field of current row while joining
-- with another field of same row
( select column_value from table(tab_field)
where column_value = tab_str_field
) same_value
from table0
/
results:
| TAB_FIELD | TAB_CARDINALITY | TAB_COUNT | SAME_VALUE |
--------------------------------------------------------
| A,B,C | 3 | 3 | A |
| B,C | 2 | 2 | B |
| A,B,C,D | 4 | 4 | C |
| A | 1 | 1 | (null) |
Example 2 (SQLFiddle) - work with constructed source data alone - OK
select 'Work with constructed source data alone - OK' caption from dual
/
with table_data_from_set as (
select
'A' tab_str_field,
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual
) as TabType0) tab_field
from dual union all
select
'B' tab_str_field,
cast(multiset(
select 'B' from dual union all
select 'C' from dual
) as TabType0) tab_field
from dual union all
select
'C' tab_str_field,
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual union all
select 'D' from dual
) as TabType0) tab_field
from dual union all
select
'D' tab_str_field,
cast(multiset(
select 'A' from dual
) as TabType0) tab_field
from dual
)
select
tab_field tab_field,
-- cardinality
cardinality(tab_field) tab_cardinality,
-- select from table field of current row
(select count(1) from table(tab_field)) tab_count,
-- select from field of current row while joining
-- with another field of same row
( select column_value from table(tab_field)
where column_value = tab_str_field
) same_value
from table_data_from_set
/
results:
| TAB_FIELD | TAB_CARDINALITY | TAB_COUNT | SAME_VALUE |
--------------------------------------------------------
| A,B,C | 3 | 3 | A |
| B,C | 2 | 2 | B |
| A,B,C,D | 4 | 4 | C |
| A | 1 | 1 | (null) |
Example 3 (SQLFiddle) - join table with multisets constructed in WITH - OK
select 'Join table with multisets constructed in WITH - OK' caption from dual
/
with table_data_from_set as (
select
'A' tab_str_field,
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual
) as TabType0) tab_field
from dual union all
select
'B' tab_str_field,
cast(multiset(
select 'B' from dual union all
select 'C' from dual
) as TabType0) tab_field
from dual union all
select
'C' tab_str_field,
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual union all
select 'D' from dual
) as TabType0) tab_field
from dual union all
select
'D' tab_str_field,
cast(multiset(
select 'A' from dual
) as TabType0) tab_field
from dual
)
select
table0.tab_field table0_tab_field,
table_data_from_set.tab_field set_tab_field,
-- cardinality
cardinality(table0.tab_field) table0_tab_cardinality,
cardinality(table_data_from_set.tab_field) set_tab_cardinality,
-- select from table field of current row
(select count(1) from table(table_data_from_set.tab_field)) set_tab_count,
-- select from field of current row while joining
-- with another field of same row
( select column_value from table(table_data_from_set.tab_field)
where column_value = table0.tab_str_field
) same_value
from
table0,
table_data_from_set
where
table_data_from_set.tab_str_field = table0.tab_str_field
/
results:
| TABLE0_TAB_FIELD | SET_TAB_FIELD | TABLE0_TAB_CARDINALITY | SET_TAB_CARDINALITY | SET_TAB_COUNT | SAME_VALUE |
----------------------------------------------------------------------------------------------------------------
| A,B,C | A,B,C | 3 | 3 | 3 | A |
| B,C | B,C | 2 | 2 | 2 | B |
| A,B,C,D | A,B,C,D | 4 | 4 | 4 | C |
| A | A | 1 | 1 | 1 | (null) |
Example 4 (SQLFiddle) - join table with multisets constructed in WITH + subquery - OK
select 'Join table with multisets constructed in WITH and subquery - OK' caption from dual
/
with table_data_from_set as (
select
'A' tab_str_field,
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual
) as TabType0) tab_field
from dual union all
select
'B' tab_str_field,
cast(multiset(
select 'B' from dual union all
select 'C' from dual
) as TabType0) tab_field
from dual union all
select
'C' tab_str_field,
cast(multiset(
select 'A' from dual union all
select 'B' from dual union all
select 'C' from dual union all
select 'D' from dual
) as TabType0) tab_field
from dual union all
select
'D' tab_str_field,
cast(multiset(
select 'A' from dual
) as TabType0) tab_field
from dual
)
select
table0_tab_field table0_tab_field,
set_tab_field set_tab_field,
-- cardinality
cardinality(table0_tab_field) table0_tab_cardinality,
cardinality(set_tab_field) set_tab_cardinality,
-- select from table field of current row
(select count(1) from table(set_tab_field)) set_tab_count,
-- select from field of current row while joining
-- with another field of same row
( select column_value from table(set_tab_field)
where column_value = table0_tab_str_field
) same_value
from (
select
table0.tab_str_field table0_tab_str_field,
table0.tab_field table0_tab_field,
table_data_from_set.tab_str_field set_tab_str_field,
table_data_from_set.tab_field set_tab_field
from
table0,
table_data_from_set
where
table_data_from_set.tab_str_field = table0.tab_str_field
)
/
results:
| TABLE0_TAB_FIELD | SET_TAB_FIELD | TABLE0_TAB_CARDINALITY | SET_TAB_CARDINALITY | SET_TAB_COUNT | SAME_VALUE |
----------------------------------------------------------------------------------------------------------------
| A,B,C | A,B,C | 3 | 3 | 3 | A |
| B,C | B,C | 2 | 2 | 2 | B |
| A,B,C,D | A,B,C,D | 4 | 4 | 4 | C |
| A | A | 1 | 1 | 1 | (null) |
Example 5 (SQLFiddle) - join table with multisets constructed on the fly - FAILED
select 'Join table with multisets constructed on the fly - FAIL (set_tab_count wrong)' caption from dual
/
with string_set as (
select 'A' str_field from dual union all
select 'B' str_field from dual union all
select 'C' str_field from dual union all
select 'D' str_field from dual union all
select 'E' str_field from dual
)
select
table0_tab_field table0_tab_field,
set_tab_field set_tab_field,
-- cardinality
cardinality(table0_tab_field) table0_tab_cardinality,
cardinality(set_tab_field) set_tab_cardinality,
-- select from table field of current row
(select count(1) from table(set_tab_field)) set_tab_count,
-- select from field of current row while joining
-- with another field of same row
( select column_value from table(set_tab_field)
where column_value = table0_tab_str_field
) same_value
from (
select
table0.tab_str_field table0_tab_str_field,
table0.tab_field table0_tab_field,
(
cast(multiset(
select
string_set.str_field
from
string_set,
table(table0.tab_field) tab_table
where
string_set.str_field = tab_table.column_value
) as TabType0)
) set_tab_field
from
table0
)
/
result (all values in set_tab_count column are same - wrong! ) :
| TABLE0_TAB_FIELD | SET_TAB_FIELD | TABLE0_TAB_CARDINALITY | SET_TAB_CARDINALITY | SET_TAB_COUNT | SAME_VALUE |
----------------------------------------------------------------------------------------------------------------
| A,B,C | A,B,C | 3 | 3 | 3 | A |
| B,C | B,C | 2 | 2 | 3 | B |
| A,B,C,D | A,B,C,D | 4 | 4 | 3 | C |
| A | A | 1 | 1 | 3 | (null) |
Oracle version information
Instance 1
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE 11.2.0.3.0 Production
TNS for IBM/AIX RISC System/6000: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
Instance 2
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Express Edition Release 11.2.0.2.0 - Production
PL/SQL Release 11.2.0.2.0 - Production
CORE 11.2.0.2.0 Production
TNS for 32-bit Windows: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production
SQLFiddle with all queries together.

Answer 1

It's a bug. Adding a /*+ NO_MERGE */ hint to the second inline view in the last example will generate the expected results. See this SQL Fiddle for an example. Regardless of the query, that hint should never change the results. There are a couple of other seemingly unrelated changes you can make that will generate the correct results, such as removing some of the columns, or adding an unused ROWNUM in the middle.
Oracle is re-writing your query to optimize it, but doing something wrong. You could probably get some more information by tracing the query, but I doubt you'll be able to truly fix the issue. Work around it for now and submit a service request to Oracle so they can create a bug and eventually fix it.