从表中的不同条件中选择COUNT

Question

我有一张名为'jobs'的桌子.对于特定用户,作业可以是活动的,存档的,过期的,挂起的或关闭的.现在每个页面请求都生成5个COUNT个查询,并且在尝试优化时我试图将其减少为单个查询.这是我到目前为止所拥有的,但它几乎比5个单独的查询快.请注意,我已经简化了每个子查询的条件,使其更容易理解,但完整查询的行为却相同.

有没有办法在不使用低效子查询的情况下在同一查询中获取这5个计数？

SELECT
  (SELECT count(*)
    FROM "jobs"
    WHERE
      jobs.creator_id = 5 AND
      jobs.status_id NOT IN (8,3,11) /* 8,3,11 being 'inactive' related statuses */
  ) AS active_count, 
  (SELECT count(*)
    FROM "jobs"
    WHERE
      jobs.creator_id = 5 AND
      jobs.due_date < '2011-06-14' AND
      jobs.status_id NOT IN(8,11,5,3) /* Grabs the overdue active jobs
                                      ('5' means completed successfully) */
  ) AS overdue_count,
  (SELECT count(*)
    FROM "jobs"
    WHERE
      jobs.creator_id = 5 AND
      jobs.due_date BETWEEN '2011-06-14' AND '2011-06-15 06:00:00.000000'
  ) AS due_today_count

这继续2个子查询,但我想你明白了.

是否有更简单的方法来收集这些数据,因为它基本上是5个不同的COUNT,来自作业表的相同数据子集？

数据子集是'creator_id = 5',之后每个计数基本上只有1-2个附加条件.请注意,目前我们正在使用Postgres,但可能会在不久的将来转向MySQL.因此,如果您能提供与ANSI兼容的解决方案,我将非常感激:)

Answer 1

这是典型的解决方案.使用案例陈述来突破不同的条件.如果记录符合它,则得到1,否则为0.然后SUM对值进行处理

  SELECT
    SUM(active_count) active_count,
    SUM(overdue_count) overdue_count
    SUM(due_today_count) due_today_count
  FROM 
  (

  SELECT 
    CASE WHEN jobs.status_id NOT IN (8,3,11) THEN 1 ELSE 0 END active_count,
    CASE WHEN jobs.due_date < '2011-06-14' AND jobs.status_id NOT IN(8,11,5,3)  THEN 1 ELSE 0 END  overdue_count,
    CASE WHEN jobs.due_date BETWEEN '2011-06-14' AND '2011-06-15 06:00:00.000000' THEN 1 ELSE 0 END  due_today_count

    FROM "jobs"
    WHERE
      jobs.creator_id = 5 ) t

更新如前所述,当0记录返回为t时,这导致所有值中的Null的单个结果.你有三个选择

1)添加A Having子句,以便您没有返回记录而不是所有NULLS的结果

   HAVING SUM(active_count) is not null

2)如果你想要返回所有零,那么你可以为你的所有总和添加合并

例如

 SELECT
      COALESCE(SUM(active_count)) active_count,
       COALESCE(SUM(overdue_count)) overdue_count
      COALESCE(SUM(due_today_count)) due_today_count

3)利用COUNT(NULL) = 0sbarro所展示的事实.您应该注意,not-null值可以是不必为1的任何值

例如

 SELECT
      COUNT(CASE WHEN 
            jobs.status_id NOT IN (8,3,11) THEN 'Manticores Rock' ELSE NULL
       END) as [active_count]

Answer 2

我会使用这种方法,将COUNT与CASE WHEN结合使用.

SELECT 
    COUNT(CASE WHEN 
        jobs.status_id NOT IN (8,3,11) THEN 1 
    END) as [Count1],
    COUNT(CASE WHEN 
        jobs.due_date < '2011-06-14' 
        AND jobs.status_id NOT IN(8,11,5,3) THEN 1
    END) as [COUNT2],
    COUNT(CASE WHEN
            jobs.due_date BETWEEN '2011-06-14' AND '2011-06-15 06:00:00.000000'
    END) as [COUNT3]
FROM 
    "jobs"
WHERE 
     jobs.creator_id = 5