postgresql出错

Question

请帮忙！

count_rate := 
(
SELECT COUNT(trate.rid) AS count_rate 
FROM tlot LEFT JOIN trate ON trate.ridlot = tlot.lid 
GROUP BY tlot.lid
);

充分：

CREATE FUNCTION editstatuswait()
  RETURNS void
LANGUAGE plpgsql
AS $$
DECLARE count_rate INTEGER;
BEGIN
  count_rate := (SELECT COUNT(trate.rid) AS count_rate FROM tlot LEFT JOIN trate ON trate.ridlot = tlot.lid GROUP BY tlot.lid);

  IF (count_rate != 0) THEN
    UPDATE tlot SET lstatus = 3
    WHERE tlot.lexpirationdate < NOW()
    AND tlot.lexpirationdate > NOW()-INTERVAL '24 hours' AND tlot.lstatus = 2;
  ELSE
    UPDATE tlot SET lstatus = 0
    WHERE tlot.lexpirationdate < NOW()
    AND tlot.lexpirationdate > NOW()-INTERVAL '24 hours' AND tlot.lstatus = 2;
  END IF;
END;
$$;

错误：[21000]错误：用作表达式的子查询返回的多行Где：SQL语句SELECT (SELECT COUNT(trate.rid) AS count_rate FROM tlot LEFT JOIN trate ON trate.ridlot = tlot.lid GROUP BY tlot.lid

我无法理解如何摆脱这个错误......

Answer 1

解决方案取决于您要实现的目标。

变量只能包含单个值，因此您尝试存储在count_rate中返回多行的子选择的结果将失败。

您必须提出一个最多返回一行的子选择（如果它不返回任何行，则将为该变量分配NULL）。

• 如果您只对第一行感兴趣（不太可能，因为没有ORDER BY），您可以将LIMIT 1附加到查询中。
• 如果你只想要某个tlot.lid的计数，你应该使用WHERE tlot.lid = ...而不是GROUP BY。
• 如果要处理多个结果，可以使用如下结构：

  FOR count_rate IN SELECT ... LOOP
     ...
  END LOOP;

Answer 2

删除GROUP BY：

count_rate := (SELECT COUNT(trate.rid) AS count_rate FROM tlot LEFT JOIN trate ON trate.ridlot = tlot.lid);

当然，这可能不符合您的意图。它至少会修复错误。