Your main problem is that column "domain" of mailboxes is specified as NOT NULL, so of course the "SET NULL" option will not work.
Here is the full message I see when I execute your code, which should be self explanatory. ERROR: null value in column "domain" violates not-null constraint DETAIL: Failing row contains (null, null, Hello). CONTEXT: SQL statement "UPDATE ONLY "public"."mailboxes" SET "username" = NULL, "domain" = NULL WHERE $1 OPERATOR(pg_catalog.=) "username" AND $2 OPERATOR(pg_catalog.=) "domain"" ********** Error ********** ERROR: null value in column "domain" violates not-null constraint SQL state: 23502 Detail: Failing row contains (null, null, Hello). Context: SQL statement "UPDATE ONLY "public"."mailboxes" SET "username" = NULL, "domain" = NULL WHERE $1 OPERATOR(pg_catalog.=) "username" AND $2 OPERATOR(pg_catalog.=) "domain""
