I have a materialized view to be created in my database. The source for the materialized view is another view in another database. I am accessing the view in source databse using a db link. My materialized view definition is pretty straightforward. Just selecting columns from the source view. DROP PUBLIC SYNONYM MVIEW; CREATE OR REPLACE PUBLIC SYNONYM MVIEW FOR MVIEW; DROP MATERIALIZED VIEW MVIEW; CREATE MATERIALIZED VIEW MVIEW TABLESPACE STGTAB PCTUSED 0 PCTFREE 10 INITRANS 2 MAXTRANS 255 STORAGE ( INITIAL 1M NEXT 1M MINEXTENTS 1 MAXEXTENTS UNLIMITED PCTINCREASE 0 BUFFER_POOL DEFAULT ) NOCACHE LOGGING NOCOMPRESS NOPARALLEL BUILD IMMEDIATE REFRESH FORCE ON DEMAND WITH PRIMARY KEY AS SELECT A, B, C, D, E, F, G, H, I, J, K, L, M FROM view@dblink WHERE GREATEST (CREATE_DATE, UPDATE_DATE) >= '07-APR-14'; When I ran this, I got the below error. "SQL Error: ORA-01427: single row subquery returns more than one row." This error occurs only when I add a particular column E to the mview definition. If I run the script without E, then it creates mview successfully. I checked the source view definition, the value for E was retrieved through a sub query, but the case was same for columns A,B,C as well but those did not throw error. Kindly help. I am thoroughly confused why this error occurred only for E. When I executed only the select statement in the mview definition, it worked fine and I could see data. But the same query when run as the mview definition threw the above error. Is the error likely to be at the source database? Thanks in advance!