将 LIMITed SELECT 和总 COUNT 组合在一起？

Question

我有一个名为profile 的表，其中包含用户信息。我需要对此表进行过滤查询并获得：

1. 与此查询匹配的行数。
2. 仅前 5000 个匹配行的数据。

我正在寻找一种最佳方式来做到这一点。显然，至少需要进行一次扫描才能进行计数，但理想情况下，数据库可以在进行计数时获取顶部匹配项。

以下查询给了我正确的结果，但它看起来有点 hacky。我想知道它是否可以做得更好？

WITH total AS (
     SELECT COUNT(*) AS total FROM profile 
         WHERE project_id = 1 and some_prop = 100)
SELECT total.total, full_name, other_prop 
    FROM profile
    INNER JOIN total ON 1 = 1
    WHERE project_id = 1 and some_prop = 100
    ORDER BY full_name ASC
    LIMIT 5000

有没有更有效的方法来做到这一点？

Answer 1

您正在扫描同一个表两次以应用过滤器。使用下面的内容，您只需在应用过滤器后扫描表格，然后在过滤后的表格上进行总计和列出。

with s as (
    select *
    from profile 
    where project_id = 1 and some_prop = 100
), t as (
    select count(*) as total from s
)
select total, full_name, other_prop 
from s cross join t
order by full_name asc
limit 5000

窗口函数版本

select
    count(*) over() as total,
    full_name,
    other_prop 
from profile
where project_id = 1 and some_prop = 100
order by full_name asc
limit 5000