Question

我有一个需要的功能：

调用另一个函数
然后返回更新语句的结果
在原子性上没有失败

该功能如下所示：

CREATE OR REPLACE FUNCTION bal_update_balances(_acct Accounts, _amount INT, _currency INT)
  RETURNS SETOF Balances AS $$
DECLARE
  --   rv SETOF Balances;
BEGIN
  -- STEP 0: initialize balances (make sure they are present in the DB)
  PERFORM bal_initialize_balances(_acct, _currency);

  -- STEP 1: update & return balances
  RETURN QUERY (
    UPDATE Balances
    SET amount   = amount + _amount,
    updated_at = now()
    WHERE id IN (SELECT id
    FROM bal_get_balances(_acct, _currency))
    RETURNING *
  );
END;
$$ LANGUAGE plpgsql;

到目前为止，我失败了：

如果我尝试将UPDATE..RETURNING的输出放在变量（rv）中，然后返回该变量：
1. 变量声明失败（rv SETOF Balances失败，invalid type name "SETOF Balances"）
2. 然后如何将UPDATE..RETURNING的输出放入rv也是一个很好的问题
如果我尝试执行RETURN QUERY，则会失败并显示syntax error at or near "UPDATE"
如果我尝试将update语句包装到select语句（SELECT * FROM (UPDATE ... RETURNING)）中，那么编译器会抱怨嵌套更新语句的SET部分（syntax error at or near "SET"）
如果我重写整个事件以迭代bal_get_balances(_acct, _currency))输出（SETOF Balances）并执行RETURN NEXT那么问题1-2再次出现，我该如何输出{ {1}}进入psql变量？

一般的想法是，我可以从主要软件（Ruby，但不相关）中运行此功能，从事务中作为各种模拟，然后根据主应用程序中某种复杂的业务逻辑决定是否去通过交易，或根据余额的确切状态将其丢弃 - 这是迄今为止我想到的将复杂和非常动态的应用业务逻辑与ACID要求相结合的唯一方式。

Answer 1

在循环中使用record类型的变量：

declare
    r record;
begin
    -- ...
    for r in 
        update balances
        set updated_at = now()
        -- ...
        returning *
    loop
        return next r;
    end loop;

Answer 2

create table t(i serial primary key, x int);
insert into t(x) select random()*10 from generate_series(1,10);

create function f() returns setof t language plpgsql as $$
declare
  r t[];
begin
  -- How to get result into the variable and return it
  with a as (update t set x = x*2 where i > 5 returning *)
    select array_agg(a.*) into r from a;
  return query select * from unnest(r);

  -- How to return result of update (just remove parenthesizes around it)
  return query
    update t set x = x*2 where i > 5 returning *;
end
$$;

select * from f();

http://rextester.com/OUZM15941

Answer 3

用CTE包裹它，就像这里：

t=# CREATE OR REPLACE FUNCTION s161()
  RETURNS SETOF s151 AS $$
DECLARE
BEGIN
  RETURN QUERY (
    with u as (UPDATE s151
    SET t= t||'***'
    RETURNING *
    )
    select * from u
  );
END;
$$ LANGUAGE plpgsql;
CREATE FUNCTION
Time: 1.109 ms
t=# begin;
BEGIN
Time: 0.117 ms
t=# select * from s161() limit 3;
       t
---------------
 s141***
 events***
 tg_rep_que***
(3 rows)

PLSQL函数如何返回UPDATED ... RETURNING查询的结果？

3 个答案: