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我是 Postgresql 的新手，我正在研究它的功能。带有条件“什么都不做”的更新/删除规则似乎打破了每个更新/删除查询的“返回子句”。从 postgresql 9.5 起有什么解决方案吗？

这是我为测试而运行的简单 sql 片段：

-- clear && dropdb --if-exists graph && createdb graph -E UTF8 -T template0 && psql graph < schema.sql

create table vertices (
    id bigserial not null primary key,
    hash char(32),
    label varchar(128) not null,
    data jsonb default '{}'
);

-- default groups and users cannot be updated or deleted --
create or replace rule preventDefaultVtxUpdate as
    on update to vertices
    where ( old.label in ('group', 'user') and old.data->>'name' in ('superadmin', 'guest') )
    do instead nothing;

create or replace rule preventDefaultVtxDelete as
    on delete to vertices
    where ( old.label in ('group', 'user') and old.data->>'name' in ('superadmin', 'guest') )
    do instead nothing;

-- default groups and users
insert into vertices (label, data) values ('group', '{"name":"superadmin"}');
insert into vertices (label, data) values ('group', '{"name":"guest"}');

insert into vertices (label, data) values ('user', '{"name":"superadmin"}');
insert into vertices (label, data) values ('user', '{"name":"guest"}');

-- try
update vertices set data = '{}' returning *;
delete from vertices returning *;

它大喊：

ERROR:  cannot perform UPDATE RETURNING on relation "vertices"
HINT:  You need an unconditional ON UPDATE DO INSTEAD rule with a RETURNING clause.
ERROR:  cannot perform DELETE RETURNING on relation "vertices"
HINT:  You need an unconditional ON DELETE DO INSTEAD rule with a RETURNING clause.

使用当前解决方案编辑：正如评论的那样，我解决了将规则重写为触发器的问题。它更丑但有效。使用以下触发器而不是规则对性能有何影响？

create table vertices (
    id bigserial not null primary key,
    hash char(32),
    label varchar(128) not null,
    data jsonb default '{}'
);

create or replace function preventDefaultVtxUpdateAndDelete() returns trigger AS $preventDefaultVtxUpdateAndDelete$
    begin
        return null;
    end
$preventDefaultVtxUpdateAndDelete$ language plpgsql;

create trigger preventDefaultVtxUpdateAndDelete
    before update or delete on vertices
    for each row
        when ( old.label in ('group', 'user') and old.data->>'name' in ('superadmin', 'guest') )
        execute procedure preventDefaultVtxUpdateAndDelete();

-- default groups and users
insert into vertices (label, data) values ('group', '{"name":"superadmin"}');
insert into vertices (label, data) values ('group', '{"name":"guest"}');

insert into vertices (label, data) values ('user', '{"name":"superadmin"}');
insert into vertices (label, data) values ('user', '{"name":"guest"}');

    insert into vertices (label, data) values ('user', '{"name":"ciao"}');

-- try
select * from vertices;
update vertices set data = '{}' returning *;
delete from vertices returning *;
select * from vertices;
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