Question

ALTER TABLE RECORDINGS ADD PRIMARY KEY (ID);

CREATE MATERIALIZED VIEW LOG ON RECORDINGS TABLESPACE USERS NOLOGGING;

DROP MATERIALIZED VIEW REC_SEARCH_TEST;
CREATE MATERIALIZED VIEW REC_SEARCH_TEST
REFRESH COMPLETE ON COMMIT
AS (
    SELECT DISTINCT ID, TITLE FROM RECORDINGS
);


ORA-12054: cannot set the ON COMMIT refresh attribute for the materialized view

Cannot understand what is wrong here, I know that if I take out the DISTINCT clause it works, but why can I not use ‘DISTINCT’ if I specify ‘REFRESH COMPLETE ON COMMIT’ which is required.

If I use DISTINCT and REFRESH on demand there is no problem, but these are not the requirements.

Answer 1

Seems like with the addition of the DISTINCT, you’ve made your view’s underlying SQL ineligible for fast refresh, and therefore not able to be used with ON COMMIT (even tho you specify refresh complete instead of refresh fast). From Oracle docs:

The two refresh execution modes are ON COMMIT and ON DEMAND. Depending
on the materialized view you create, some of the options may not be
available. Table 8-4 describes the refresh modes.

Table 8-4 Refresh Modes

ON COMMIT

Refresh occurs automatically when a transaction that modified one of
the materialized view’s detail tables commits. This can be specified
as long as the materialized view is fast refreshable (in other words,
not complex). The ON COMMIT privilege is necessary to use this mode.

ON DEMAND

Refresh occurs when a user manually executes one of the available
refresh procedures contained in the DBMS_MVIEW package (REFRESH,
REFRESH_ALL_MVIEWS, REFRESH_DEPENDENT).

The same document link has a list of restrictions for fast refresh as well.