Realmente no puedo explicar por qué , pero hice una observación que puede hacerle una solución alternativa el problema.
Aquí está el resultado de explain_mview para la consulta de tu MV
exec dbms_mview.explain_mview(q'[select A.y, B.z from A join B on A.x = B.x]');
SELECT capability_name, possible, SUBSTR(related_text,1,8)
AS rel_text, SUBSTR(msgtxt,1,60) AS msgtxt
FROM MV_CAPABILITIES_TABLE
WHERE capability_name like '%REWRITE%'
ORDER BY seq;
CAPABILITY_NAME P REL_TEXT MSGTXT
------------------------------ - -------- ------------------------------------------------------------
REWRITE Y
REWRITE_FULL_TEXT_MATCH Y
REWRITE_PARTIAL_TEXT_MATCH Y
REWRITE_GENERAL N the reason why the capability is disabled has escaped analys
REWRITE_PCT N general rewrite is not possible or PCT is not possible on an
El problema es IMO en el REWRITE_GENERAL = 'N'
Si repites el mismo explain_mview solo usando POJO (=combinación simple y antigua en Oracle) verá un resultado diferente.
truncate table mv_capabilities_table;
exec dbms_mview.explain_mview(q'[select A.y, B.z from A, B where A.x = B.x]');
CAPABILITY_NAME P REL_TEXT MSGTXT
------------------------------ - -------- ------------------------------------------------------------
REWRITE Y
REWRITE_FULL_TEXT_MATCH Y
REWRITE_PARTIAL_TEXT_MATCH Y
REWRITE_GENERAL Y
REWRITE_PCT N general rewrite is not possible or PCT is not possible on an
PCT_TABLE_REWRITE N A relation is not a partitioned table
PCT_TABLE_REWRITE N B relation is not a partitioned table
Nuevamente importante `REWRITE_GENERAL ='Y'.
Tenga en cuenta que estoy usando 18.4 XE y esto es muy sospechoso y debe aclararse con Oracle Support.
Las buenas noticias finales es, si define el MV con la unión de Oracle , puede usar la unión ASNI y verá la reescritura:
Ejemplo
create materialized view MV2
enable query rewrite
as
select
A.y, B.z from A, B where A.x = B.x
EXPLAIN PLAN SET STATEMENT_ID = 'jara1' into plan_table FOR
select A.y, B.z from A join B on A.x = B.x where y = 'A' and z = 'Z'
;
SELECT * FROM table(DBMS_XPLAN.DISPLAY('plan_table', 'jara1','ALL'));
-------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 3846 | 15384 | 456 (8)| 00:00:01 |
|* 1 | MAT_VIEW REWRITE ACCESS FULL| MV2 | 3846 | 15384 | 456 (8)| 00:00:01 |
-------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("MV2"."Z"='Z' AND "MV2"."Y"='A')
