如何重写此 MySQL 查询以返回计数？

Question

我有这个查询：

SELECT accounts.id
FROM accounts
  LEFT JOIN account_properties ON account_properties.account_id = accounts.id
GROUP BY accounts.id
HAVING COUNT(account_properties.id) = 0

它returns 其帐户没有任何帐户属性的所有帐户 ID 的列表。如何获取没有属性的所有帐户的数量？

SELECT COUNT(accounts.id)
FROM accounts
  LEFT JOIN account_properties ON account_properties.account_id = accounts.id
GROUP BY accounts.id
HAVING COUNT(account_properties.id) = 0

这不起作用，只有 returns 1 的列表。

Answer 1

    select count(*) from (SELECT accounts.id
    FROM accounts
    LEFT JOIN account_properties ON account_properties.account_id = accounts.id
    WHERE exists account_properties.id
    GROUP BY accounts.id)

Answer 2

您可能会发现这些查询更快...假设 id 是帐户的唯一标识符。

对于 ids:

   SELECT accounts.id
     FROM accounts
LEFT JOIN account_properties ON account_properties.account_id = accounts.id
    WHERE account_properties.id IS NULL

对于ids的计数：

   SELECT COUNT(*)
     FROM accounts
LEFT JOIN account_properties ON account_properties.account_id = accounts.id
    WHERE account_properties.id IS NULL

Answer 3

SELECT `ap`.account_id IS NULL AS noProperties
   , COUNT(DISTINCT `a`.id) AS accountCount
FROM `accounts` AS `a`
  LEFT JOIN `account_properties` AS `ap` N `ap`.account_id = `a`.id
GROUP BY noProperties
HAVING noProperties
;

GROUP BY 获取有和没有属性的帐户数量，HAVING 过滤结果，以便最终结果中只有没有属性个帐户的计数。

如何重写此 MySQL 查询以返回计数？

How can I rewrite this MySQL query for returning a count?

java

mysql

sql

jdbc