postgresql - 如何在触发器函数中选择多个变量？

Question

这是我想要实现的:

CREATE FUNCTION f() RETURNS trigger AS $$
  BEGIN
    SELECT COUNT(*) AS total_num, SUM(width) AS total_width
    FROM some_table WHERE foo = NEW.foo;
    IF total_num > 0 AND total_width > 100
    THEN
      RAISE EXCEPTION 'this is bad';
    END IF;
    RETURN NEW;
  END;
$$ LANGUAGE plpgsql;

但它在语法上还不正确。

我读过我首先需要DECLARE 变量(在本例中为total_num 和total_width)所以我可以使用它们并使用SELECT INTO 但我见过只有一个变量/SELECT 语句的示例。如果我有更多呢？

Answer 1

你可以列出multiple variables在 into 部分。和 declare section需要在第一个 begin 之前出现:

CREATE FUNCTION f() RETURNS trigger 
AS $$
declare
  total_num bigint;
  total_width bigint;
BEGIN
   SELECT COUNT(*), SUM(width)
       into total_num, total_width
   FROM some_table 
   WHERE foo = NEW.foo;

   IF total_num > 0 AND total_width > 100 THEN
      RAISE EXCEPTION 'this is bad';
   END IF;
   RETURN NEW;
END;
$$ LANGUAGE plpgsql;