I noticed the following two issues while looking at the code that handles REFRESH MATERIALIZED VIEW CONCURRENTLY (refresh_by_match_merge() in matview.c):
1.
At the beginning of the function, there is some code that checks for duplicate rows, but it does not catch the following case:
CREATE TABLE t(a text, b text); INSERT INTO t VALUES('test', null); CREATE MATERIALIZED VIEW m AS SELECT * FROM t; CREATE UNIQUE INDEX ON m(a); INSERT INTO t VALUES('test', null); -- t now contains two identical rows
REFRESH MATERIALIZED VIEW CONCURRENTLY m; -> no error, but m still contains only one row! REFRESH MATERIALIZED VIEW m; -> error (as expected)
Thank you for the pointers, I made a patch in refresh_by_match_merge() which reports an error in the REFRESH MATERIALIZED VIEW CONCURRENTLY case too.
The issue was REFRESH MATERIALIZED VIEW CONCURRENTLY was incorrectly skipping duplicate detection for rows containing any NULL values. This was happening because the "WHERE newdata.* IS NOT NULL" condition returns false if any column contains NULL. My patch removes the "IS NOT NULL" preconditions from the duplicate detection query. The query now correctly checks all rows using the record equality operator (*=), which treats NULL as equal to NULL (i.e True).
Here is the output with my patch: postgres=# CREATE TABLE t(a text, b text); CREATE TABLE postgres=# INSERT INTO t VALUES('test', null); INSERT 0 1 postgres=# postgres=# CREATE MATERIALIZED VIEW m AS SELECT * FROM t; SELECT 1 postgres=# postgres=# CREATE UNIQUE INDEX ON m(a); CREATE INDEX postgres=# SELECT * FROM m; a | b ------+--- test | (1 row)
postgres=# SELECT * FROM t; a | b ------+--- test | (1 row)
postgres=# INSERT INTO t VALUES('test', null); INSERT 0 1 postgres=# SELECT * FROM t; a | b ------+--- test | test | (2 rows)
postgres=# SELECT * FROM m; a | b ------+--- test | (1 row)
postgres=# REFRESH MATERIALIZED VIEW CONCURRENTLY m; 2026-02-11 15:57:46.751 PST [39510] ERROR: new data for materialized view "m" contains duplicate rows 2026-02-11 15:57:46.751 PST [39510] DETAIL: Row: (test,) 2026-02-11 15:57:46.751 PST [39510] STATEMENT: REFRESH MATERIALIZED VIEW CONCURRENTLY m; ERROR: new data for materialized view "m" contains duplicate rows DETAIL: Row: (test,) postgres=# postgres=# REFRESH MATERIALIZED VIEW m; 2026-02-11 15:57:55.877 PST [39510] ERROR: could not create unique index "m_a_idx" 2026-02-11 15:57:55.877 PST [39510] DETAIL: Key (a)=(test) is duplicated. 2026-02-11 15:57:55.877 PST [39510] STATEMENT: REFRESH MATERIALIZED VIEW m; ERROR: could not create unique index "m_a_idx" DETAIL: Key (a)=(test) is duplicated. postgres=#
