具有PERFORM数据修改CTE查询的Postgres plpgsql [英] Postgres plpgsql with PERFORM data-modifying CTE queries

问题描述

我尝试在下面的代码示例中模拟我的问题.在下面的代码中，我在过程中执行delete from test2.效果很好:

I tried to simulate my problem in the code example below. In the code below, I am doing a delete from test2 in a procedure. This works great:

但是，就我而言，此delete是相当复杂的CTE的一部分，具有多个更新和插入(没有选择，因此我将虚拟select 1作为主查询添加).让我们对此进行模拟:

However, in my case, this delete is part of a rather complex CTE with several updates and inserts (there are no selects so I add a dummy select 1 as main query). Let's simulate this as this:

with my_cte as(delete from test2) select 1

现在，我们知道，我们必须使用perform关键字来执行此操作:

Now, as we know, we have to use the perform keyword to execute this:

perform (with my_cte as(delete from test2) select 1);

我遇到以下错误:

ERROR: WITH clause containing a data-modifying statement must be at the top level

这是plpgsql的限制吗?

Is this a limitation of plpgsql?

(请注意，这只是一个解释我的问题的示例.我知道查询实际上没有任何意义.)

(Please note that this is just an example to explain my problem. I know the queries do not really make any sense.)

create table test
(
    key int primary key  
);

create table test2
(
    key int primary key
);

create function test() returns trigger as
$$
begin
    raise notice 'hello there';
    -- this does work
    delete from test2;
    -- this doesn't work
    perform (with my_cte as(delete from test2) select 1);
    return new;
end;
$$
language plpgsql;

create trigger test after insert on test for each row execute procedure test();

insert into test(key) select 1;

推荐答案

您可以使用CTE组合多个返回查询的DELETE，INSERT，UPDATE.而且您不需要执行它，例如:

You can use CTE for combining several DELETE, INSERT, UPDATE returning queries. And you dont need perform for it, eg:

t=# begin; do $$ begin with d as (delete from s133 returning *) insert into s133 select * from d; raise info '%',(select count(1) from s133);
end; $$; commit;
BEGIN
Time: 0.135 ms
INFO:  4
DO
Time: 0.469 ms
COMMIT
Time: 0.887 ms
t=# select count(1) from s133;
 count
-------
     4
(1 row)

在这里我删除四行，并在CTE中将它们重新插入

here I delete four rows and in CTE insert them back

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