Materialized view showing red cross in front of it in SQL developer

Question

we created a materialized view in oracle database,it works fine, and other views that select on  it return results and work fine too. But it has a red cross in front of it in oracle developer.
I then refresh the view, or recreate the view, it shows green, but after a while when I come back, the red cross show up again.
What does it mean, any error message we can find?
Thanks

Answer 1

878566 wrote:
we created a materialized view in oracle database,it works fine, and other views that select on  it return results and work fine too. But it has a red cross in front of it in oracle developer.
I then refresh the view, or recreate the view, it shows green, but after a while when I come back, the red cross show up again.
What does it mean, any error message we can find?
It means your system is working NORMALLY! There is no 'error message' to find because there is no error. What you describe is EXACTLY how MVs are designed to work.
It is NORMAL for MVs to be, and to become, invalid, especially if there refresh setting is ON DEMAND. Don't confuse 'validity' with 'staleness'; they are very different things.
See the section 'Invalidating Materialized Views' in the Data Warehousing Guide'
http://docs.oracle.com/cd/B28359_01/server.111/b28313/advmv.htm#i1007082
Invalidating Materialized Views
Dependencies related to materialized views are automatically maintained to ensure correct operation. When a materialized view is created, the materialized view depends on the detail tables referenced in its definition. Any DML operation, such as an INSERT, or DELETE, UPDATE, or DDL operation on any dependency in the materialized view will cause it to become invalid. To revalidate a materialized view, use the ALTER MATERIALIZED VIEW COMPILE statement.
A materialized view is automatically revalidated when it is referenced. In many cases, the materialized view will be successfully and transparently revalidated. However, if a column has been dropped in a table referenced by a materialized view or the owner of the materialized view did not have one of the query rewrite privileges and that privilege has now been granted to the owner, you should use the following statement to revalidate the materialized view:
ALTER MATERIALIZED VIEW mview_name COMPILE; 
The state of a materialized view can be checked by querying the data dictionary views USER_MVIEWS or ALL_MVIEWS. The column STALENESS will show one of the values FRESH, STALE, UNUSABLE, UNKNOWN, UNDEFINED, or NEEDS_COMPILE to indicate whether the materialized view can be used. The state is maintained automatically. However, if the staleness of a materialized view is marked as NEEDS_COMPILE, you could issue an ALTER MATERIALIZED VIEW ... COMPILE statement to validate the materialized view and get the correct staleness state. If the state of a materialized view is UNUSABLE, you must perform a complete refresh to bring the materialized view back to the FRESH state. If the materialized view is based on a prebuilt table that you never refresh, you will need to drop and re-create the materialized view.
As the doc states Oracle will normally 'revalidate' an MV when it is referenced. You can do this manually by using 'ALTER . . . COMPILE'. For an ON DEMAND MV compiling it will NOT alter the contents of the MV - it may stil be STALE.
You don't need to REFRESH or recreate the MV to make it valid; just recompile it. If it doesn't become VALID after you compile it then there is usually an issue with one of the dependent objects that you need to resolve.