如何使用许多相同的选择优化 SQL 查询

Question

我已经创建了这个查询，但我认为它可以进行大量优化......但我不知道怎么做？

这是一个查询，它选择了

学生拥有的未完成任务，还选择了计划的任务计数，以及他请求帮助的任务数。

后来我不想要计数，而是他/她请求帮助的答案的整行，但现在我从计数开始，因为这似乎更容易。

有没有人可以解释我如何优化这一点，或者我可以在哪里学习？

SELECT
    gu.user_id,
    notComplete.count AS notComplete,
    planned.count AS planned,
    helpNeeded.need AS helpNeeded
FROM
    `groups_users` gu
LEFT JOIN(
    SELECT
        a.created_by AS user_id,
        COUNT(1) AS 'count'
    FROM
        `answers` a
    WHERE
        a.deleted_at IS NULL AND a.completed_at IS NULL AND a.checked_at IS NULL
    GROUP BY
        a.created_by
) AS notComplete
ON
    notComplete.user_id = gu.user_id
LEFT JOIN(
    SELECT
        a.created_by AS user_id,
        COUNT(1) AS 'count'
    FROM
        `answers` a
    WHERE
        a.deleted_at IS NULL
    GROUP BY
        a.created_by
) AS planned
ON
    planned.user_id = gu.user_id
LEFT JOIN(
    SELECT
        a.created_by AS user_id,
        COUNT(1) AS need
    FROM
        `answers` a
    WHERE
        a.deleted_at IS NULL AND a.requested_help_at IS NOT NULL
    GROUP BY
        a.created_by
) AS helpNeeded
ON
    helpNeeded.user_id = gu.user_id
INNER JOIN `users` u ON
    u.id = gu.user_id AND u.type = 'student'
WHERE
    gu.group_id = 213

Answer 1

尝试以下操作

SELECT
  gu.user_id,
  SUM(IF(a.deleted_at IS NULL AND a.completed_at IS NULL AND a.checked_at IS NULL,1,0)) AS notComplete,
  SUM(IF(a.deleted_at IS NULL,1,0)) AS planned,
  SUM(IF(a.deleted_at IS NULL AND a.requested_help_at IS NOT NULL,1,0)) AS helpNeeded
FROM `groups_users` gu
JOIN `users` u ON u.id = gu.user_id
LEFT JOIN `answers` a ON a.created_by = gu.user_id
WHERE gu.group_id = 213
  AND u.type = 'student'
GROUP BY gu.user_id

针对第二个问题尝试以下操作

SELECT
  gu.user_id,
  IF(a.deleted_at IS NULL AND a.completed_at IS NULL AND a.checked_at IS NULL,1,0) AS notComplete,
  IF(a.deleted_at IS NULL,1,0) AS planned,
  IF(a.deleted_at IS NULL AND a.requested_help_at IS NOT NULL,1,0) AS helpNeeded,
  a.* -- full answer row
FROM `groups_users` gu
JOIN `users` u ON u.id = gu.user_id
LEFT JOIN `answers` a ON a.created_by = gu.user_id
LEFT JOIN `answer_plannedday` ap ON ap.answer_id = a.id
LEFT JOIN `plannedday` p ON p.id = ap.planned_day_id
WHERE gu.group_id = 213
  AND u.type = 'student'  
  AND STR_TO_DATE(CONCAT(p.year, '-', p.month, '-', p.day), '%Y-%m-%d') BETWEEN STR_TO_DATE('2016-12-01', '%Y-%m-%d') AND STR_TO_DATE('2018-04-13', '%Y-%m-%d')

如果您只想获取 notComplete 的详细信息，您可以将所有必要条件放入 WHERE 中

SELECT
  gu.user_id,
  a.* -- full answer row
FROM `groups_users` gu
JOIN `users` u ON u.id = gu.user_id
LEFT JOIN `answers` a ON a.created_by = gu.user_id
LEFT JOIN `answer_plannedday` ap ON ap.answer_id = a.id
LEFT JOIN `plannedday` p ON p.id = ap.planned_day_id
WHERE gu.group_id = 213
  AND u.type = 'student'  
  AND STR_TO_DATE(CONCAT(p.year, '-', p.month, '-', p.day), '%Y-%m-%d') BETWEEN STR_TO_DATE('2016-12-01', '%Y-%m-%d') AND STR_TO_DATE('2018-04-13', '%Y-%m-%d')
  -- you say here that you want to get only these rows
  AND a.deleted_at IS NULL AND a.completed_at IS NULL AND a.checked_at IS NULL