mysql - 使用 SQL_CALC_FOUND_ROWS 和 UNION ALL 的 Select 语句

Question

因此，我正在查找绑定(bind)到电子邮件和 account_id 的数据，如果没有结果，则仅查找 account_id。下面的代码可以正确执行此操作。

 SELECT SQL_CALC_FOUND_ROWS account_id, email, latitude, longitude
 FROM call_module_location
 WHERE email = $email AND `account_id` = $account_id
 UNION ALL
 SELECT account_id, email, latitude, longitude
 FROM call_module_location
 WHERE  FOUND_ROWS() = 0 AND `account_id` = $account_id

但是我需要处理3种情况，如果也找不到id数据，在这种情况下我应该通过电子邮件获取数据:

  SELECT SQL_CALC_FOUND_ROWS account_id, email, latitude, longitude
  FROM call_module_location
  WHERE email = $email AND `account_id` = $account_id
  UNION ALL
  SELECT account_id, email, latitude, longitude
  FROM call_module_location
  WHERE  FOUND_ROWS() = 0 AND `account_id` = $account_id
  UNION ALL
  SELECT account_id, email, latitude, longitude
  FROM call_module_location
  WHERE FOUND_ROWS() = 0 AND email = $email";

但是它不起作用。有什么解决办法吗？

Answer 1

SELECT account_id, email, latitude, longitude
FROM (SELECT 1 priority, account_id, email, latitude, longitude
      FROM call_module_location
      WHERE email = $email AND `account_id` = $account_id
      UNION
      SELECT 2 priority, account_id, email, latitude, longitude
      FROM call_module_location
      WHERE `account_id` = $account_id
      UNION
      SELECT 3 priority, account_id, email, latitude, longitude
      FROM call_module_location
      WHERE email = $email) u
ORDER BY priority
LIMIT 1

如果您将 SQL_CALC_FOUND_ROWS 添加到 UNION 中的第二个查询，您的原始查询也可能会起作用。