在一个

Question

我有三个表：users，accounts和scores。每个查询实际上都给了我想要的结果：

-- This will return all user ids with a count of "calculated" scores
SELECT u.id AS user_id, count(1) AS total FROM scores s
  INNER JOIN accounts a ON s.account_id = a.id
  INNER JOIN user u ON a.user_id = u.id
WHERE s.status = 'CALCULATED'
GROUP BY user_id;

-- This will return all user ids with a count of non-calculated scores
SELECT u.id AS user_id, count(1) AS failures FROM scores s
  INNER JOIN accounts a ON s.account_id = a.id
  INNER JOIN user u ON a.user_id = u.id
WHERE s.status <> 'CALCULATED'
GROUP BY user_id;

但我想回复这样的内容：user id，total，failures ...全部在一个查询中！

Answer 1

这可以通过条件聚合来完成。 SUM中的条件根据满足的条件返回1或0。

SELECT u.id AS user_id,
SUM(s.status='CALCULATED'),
SUM(s.status<>'CALCULATED') AS total 
FROM scores s
INNER JOIN accounts a ON s.account_id = a.id
INNER JOIN user u ON a.user_id = u.id
GROUP BY u.id;

Answer 2

作为一个注释，您可以简化查询，因为（大概）不需要user表：

SELECT a.user_id,
       SUM(s.status = 'CALCULATED') as num_calc,
       SUM(s.status <> 'CALCULATED') AS num_notcalc 
FROM scores s INNER JOIN
     accounts a
     ON s.account_id = a.id
GROUP BY a.user_id;

您的查询给出了正确的答案，但您可能还需要注意NULL值。如果这是一个问题，请使用<=> NULL - 安全等值运算符：

SELECT a.user_id,
       SUM(s.status = 'CALCULATED') as num_calc,
       SUM(NOT s.status <=> 'CALCULATED') AS num_notcalc 
FROM scores s INNER JOIN
     accounts a
     ON s.account_id = a.id
GROUP BY a.user_id;