Question

我有这个按人返回帐号的查询

SELECT p.id, COUNT(a.id) accounts
FROM Person p
  LEFT JOIN Account a
  ON a.person_id = p.id
WHERE p.id = 1
GROUP BY p.id;

它找不到。如果此人有两个帐户，则会为帐户返回2。但我还需要一个活跃的帐户计数。我试着这样做：

SELECT p.id, COUNT(a.id) accounts, COUNT(a1.id) active_accounts
FROM Person p
  LEFT JOIN Account a
  ON a.person_id = p.id
  LEFT JOIN Account a1
  ON a1.person_id = p.id AND a1.state = '0'
WHERE p.id = 1
GROUP BY p.id;

但是此查询为帐户返回4而不是2。如何解决此问题？

Answer 1

您的查询生成笛卡尔积，每个帐户都与其他帐户一起

您需要一次加入：

SELECT
   p.id,
   COUNT(a.id) total_accounts,
   sum(case when a1.state = '0' then 0 else 1 end) inactive_accounts,
   sum(case when a1.state = '0' then 1 else 0 end) active_accounts
FROM Person p
  LEFT JOIN Account a
  ON a.person_id = p.id
WHERE p.id = 1
GROUP BY p.id;

Answer 2

你可以用它。我假设state ='0'表示活动。

SELECT p.id, COUNT(a.id) accounts, SUM(CASE WHEN a.state = '0' THEN 1 ELSE 0 END) active_accounts
FROM Person p
  LEFT JOIN Account a
  ON a.person_id = p.id
WHERE p.id = 1
GROUP BY p.id;

如何通过不同的条件两次加入同一个表来获得正确的＆＃34; group by＆＃34;结果

2 个答案: