postgresql - 简单的 postgres 函数

Question

我尝试在 postgres 中声明简单的函数，但我无法让它工作。它看起来像这样:

CREATE OR REPLACE FUNCTION test2(rok int, id int)
  RETURNS int AS $$
BEGIN
select sum(data_zakonczenia-data_rozpoczecia) from historia where id_eksponatu = $2 AND data_rozpoczecia>DATE(to_char($1,'9999') || '-01-01') AND data_zakonczenia<DATE(to_char($1+1,'9999') || '-01-01');
END;
$$ LANGUAGE 'plpgsql';

出现以下错误

ERROR:  query has no destination for result data
PODPOWIEDŹ:  If you want to discard the results of a SELECT, use PERFORM instead.
KONTEKST:  PL/pgSQL function "test2" line 2 at SQL statement

我不确定如何让它工作。

Answer 1

你想要一个 SQL 函数:

CREATE OR REPLACE FUNCTION test2(rok int, id int)
  RETURNS int AS 
$$
   select sum(data_zakonczenia-data_rozpoczecia) 
   from historia where id_eksponatu = $2 
    AND data_rozpoczecia>DATE(to_char($1,'9999') || '-01-01') 
    AND data_zakonczenia<DATE(to_char($1+1,'9999') || '-01-01');
$$ LANGUAGE sql;

或者如果你出于某种原因需要PL/pgSQL，你需要使用return query

CREATE OR REPLACE FUNCTION test2(rok int, id int)
  RETURNS int AS $$
BEGIN
  return query
    select sum(data_zakonczenia-data_rozpoczecia) 
    from historia where id_eksponatu = $2 
     AND data_rozpoczecia>DATE(to_char($1,'9999') || '-01-01') 
     AND data_zakonczenia<DATE(to_char($1+1,'9999') || '-01-01');
END;
$$ LANGUAGE plpgsql;

或者如果您需要在返回之前对值做一些事情:

CREATE OR REPLACE FUNCTION test2(rok int, id int)
  RETURNS int AS $$
declare 
   l_sum integer;
BEGIN
  select sum(data_zakonczenia-data_rozpoczecia) 
      into l_sum
  from historia where id_eksponatu = $2 
   AND data_rozpoczecia>DATE(to_char($1,'9999') || '-01-01') 
   AND data_zakonczenia<DATE(to_char($1+1,'9999') || '-01-01');

   ....

  return l_sum;         
END;
$$ LANGUAGE plpgsql;

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