'having子句'中的未知列

Question

我需要在sakila数据库中找到电影的最长租期.我试过这个:

  SELECT DISTINCT
      customer.first_name
    FROM
      rental,
      customer
    WHERE
      rental.customer_id = customer.customer_id
    GROUP BY
      rental.rental_id
    HAVING
      (
        rental.return_date - rental.rental_date
      ) =(
      SELECT
        MAX(countRental)
      FROM
        (
        SELECT
          (
            rental.return_date - rental.rental_date
          ) AS countRental
        FROM
          rental,
          customer
        GROUP BY
          rental.rental_id
      ) AS t1
    )

但我收到错误:

1054 - 'having子句'中的未知列'rental.return_date'

有谁知道为什么？我使用了一个应该是聚合数据的列..我缺少什么

Answer 1

如文档中所述

SQL标准要求HAVING必须仅引用GROUP BY子句中的列或聚合函数中使用的列.但是,MySQL支持对此行为的扩展,并允许HAVING引用SELECT列表中的列和外部子查询中的列.

您必须在select子句中指定return_date和rental_date.

有两种选择:

SELECT DISTINCT
  customer.first_name,
  rental.return_date,
  rental.rental_date
FROM
  rental,
  customer
WHERE
  rental.customer_id = customer.customer_id
GROUP BY
  rental.rental_id
HAVING
  (
    rental.return_date - rental.rental_date
  ) =(
  ...

要么

SELECT DISTINCT
  customer.first_name,
  (rental.return_date - rental.rental_date) as rental_duration
FROM
  rental,
  customer
WHERE
  rental.customer_id = customer.customer_id
GROUP BY
  rental.rental_id
HAVING
  rental_duration =(
  ...

两者都应该工作得很好.