CREATE TABLE TEST_MERGE_PT (
    LIST_ID  INTEGER NOT NULL,
    TYPE_ID  INTEGER DEFAULT 0 NOT NULL,
    OBJ_ID   INTEGER NOT NULL
);
ALTER TABLE TEST_MERGE_PT ADD CONSTRAINT PKTEST_MERGE_PT PRIMARY KEY (LIST_ID, TYPE_ID, OBJ_ID);

    merge into test_merge_pt d
    using (
        select
            3 as lid,
            1 as id,
            0 as tid
        from rdb$database
        union all
        select
            3 as lid,
            1 as id,
            0
        from rdb$database
    ) s
    on d.list_id = s.lid and d.obj_id = s.id and d.type_id = s.tid
    when not matched then
        insert (list_id, obj_id, type_id)
        values (s.lid, s.id, s.tid);

Invalid insert or update value(s): object columns are constrained - no 2 table rows can have duplicate column values.
violation of PRIMARY or UNIQUE KEY constraint "PKTEST_MERGE_PT" on table "TEST_MERGE_PT".
Problematic key value is ("LIST_ID" = 3, "TYPE_ID" = 0, "OBJ_ID" = 1).

Server Version: LI-V3.0.4.33047 Firebird 3.0
Server Implementation: Firebird/Linux/AMD/Intel/x64
Service Version: 2