If you ever tried to refresh materialized view and got an error like this:
BEGIN dbms_mview.refresh('MYMVIEW'); END;
ERROR at line 1:
ORA-00942: table or view does not exist
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 2256
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 2462
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 2431
ORA-06512: at line 1
then it's probably because your schema was created by exporting and importing data from schema with another name. If you examine the content of a schema dump file like this:
$ exp myschema@$ORACLE_SID file=myschema rows=n statistics=none
$ strings myschema.dmp|less
then you may see undocumented arguments in commands that create materialized views:
CREATE SNAPSHOT "MYMVIEW" USING ("MYMVIEW", (8, 'DB.GLOBAL.NAME', 1, 0, 0, "MYSCHEMA", ...
The string "DB.GLOBAL.NAME" is obviously a global database name where you exported schema from. It is followed by a few digits and a name of the exported schema. There is also a lot of other stuff I have no idea about, but that probably does not matter.
The point is that if you import a dump file into schema with different name the "MYSCHEMA" argument will not be changed. So when you later try to refresh that materialized view Oracle will search for tables in schema "MYSCHEMA" instead of the current schema. And this is how we can get "ORA-00942: table or view does not exist" error.
So to fix that we should find where that "MYSCHEMA" is stored in the database and change it to the name of the schema the data was imported into. It turns out that it is stored in two tables: "SYS.SNAP$" and "SYS.SNAP_REFTIME$". Basically you need to connect to your database as SYSDBA and execute the following queries:
update SYS.SNAP$ set MOWNER=SOWNER where MOWNER<>SOWNER;
update SYS.SNAP_REFTIME$ set MOWNER=SOWNER where MOWNER<>SOWNER;
Of course you should examine contents of those tables before executing these queries in case there is a legitimate reason for some materialized views to have differences in those values. Disclaimer:
I have no responsibility for this advice. If you crashed a production database executing code you found on a fan site you have no one to blame but yourself.
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