Sql计数返回错误的数字

Question

我有一个api我打电话，我需要很多来自不同表的数据，所以我使用连接，现在的问题是，虽然我有4个回复，5个交互数据总是返回20个回复和20个交互这是结果：

screen_name screen_state replies interactions alerts
sjerd       0            20      20           0

我使用此查询来计算记录和结果：

   SELECT u.screen_name,
          u.screen_state,
          count(r.id) AS replies,
          count(i.id) AS interactions,
          count(a.alerts) AS alerts
   FROM   users u 
   LEFT   JOIN reply r ON u.id = r.user 
   LEFT   JOIN interactions i ON u.id = i.user_id 
   LEFT   JOIN alerts a ON u.id = a.user_id WHERE u.id ='2' 
   GROUP  BY u.id, u.screen_state

有人可以看到为什么它返回20，而我在回复表中总共只有7行回复，并且在交互表中共有5行交互。 每一行都是1个反应或回复。

Answer 1

您的计数总是会得到相同的结果，因为所有表都在同一级别加入。

您需要将计数作为内联子查询（或者其他任何 - 我永远不会记住正确的术语）：

SELECT u.screen_name,
       u.screen_state,
       (select count(*) from reply r where u.id = r.user) AS replies,
       (select count(*) from interactions i where u.id = i.user_id) AS interactions,
       (select count(*) from alerts a where u.id = a.user_id) AS alerts
FROM   users u
WHERE u.id ='2' 

Answer 2

   SELECT u.screen_name, u.screen_state, 
   count(DISTINCT r.id) AS replies,
   count(DISTINCT i.id) AS interactions,
   count(DISTINCT a.alerts) AS alerts 
   FROM users u 
   LEFT JOIN reply r ON u.id = r.user 
   LEFT JOIN interactions i ON u.id = i.user_id 
   LEFT JOIN alerts a ON u.id = a.user_id WHERE u.id ='2' 
   GROUP BY u.id, u.screen_state