相关疑难解决方法(0)

我需要按日期/时间字段对PostgreSQL表进行排序,例如last_updated.

但是,该字段允许为空或空,我想与空记录last_updated来之前,非空last_updated.
这可能吗？

order by last_updated asc /* and null last_updated records first ?? */

我在PostgreSQL中有以下查询:

SELECT 
    COUNT(a.log_id) AS overall_count
FROM 
    "Log" as a, 
    "License" as b 
WHERE 
    a.license_id=7 
AND 
    a.license_id=b.license_id 
AND
    b.limit_call > overall_count
GROUP BY 
    a.license_id;

为什么我会收到此错误:

错误:列"overall_count"不存在

我的表结构:

License(license_id, license_name, limit_call, create_date, expire_date)
Log(log_id, license_id, log, call_date)

我想检查许可证是否已达到特定月份的通话限制.

我有一个工作查询,按硬件模型和结果对数据进行分组,但问题是有很多"结果".我试图将其减少到"如果结果= 0然后保持为0,否则将其设置为1".这通常有效,但我最终得到:

    day     |      name      | type | case | count
------------+----------------+------+------+-------
 2013-11-06 | modelA         |    1 |    0 |   972
 2013-11-06 | modelA         |    1 |    1 |    42
 2013-11-06 | modelA         |    1 |    1 |     2
 2013-11-06 | modelA         |    1 |    1 |    11
 2013-11-06 | modelB         |    1 |    0 |   456
 2013-11-06 | modelB         |    1 |    1 |    16
 2013-11-06 | modelB         |    1 |    1 |     8
 2013-11-06 …

我正在从 Postgres 表中聚合数据，查询大约需要 2 秒，我想将其减少到不到一秒。

请在下面找到执行细节：

询问

select
    a.search_keyword,
    hll_cardinality( hll_union_agg(a.users) ):: int as user_count,
    hll_cardinality( hll_union_agg(a.sessions) ):: int as session_count,
    sum(a.total) as keyword_count
from
    rollup_day a
where
    a.created_date between '2018-09-01' and '2019-09-30'
    and a.tenant_id = '62850a62-19ac-477d-9cd7-837f3d716885'
group by
    a.search_keyword
order by
    session_count desc
limit 100;

表元数据

1. 总行数 - 506527
2. 列上的复合索引：tenant_id 和 created_date

查询计划

Custom Scan (cost=0.00..0.00 rows=0 width=0) (actual time=1722.685..1722.694 rows=100 loops=1)
  Task Count: 1
  Tasks Shown: All
  ->  Task
        Node: host=localhost port=5454 dbname=postgres
        ->  Limit  (cost=64250.24..64250.49 …