使用 SQL CTE 替换多个临时表

Question

我最近被介绍给 SQL CTE，我想在这里实现一个，但我不太确定如何使用此查询中的两个不同表来实现这一点。下面的查询确实让我得到了我需要的结果，只需要 2 秒就可以运行，但是，我觉得 CTE 是可行的方法，但我需要帮助：

ALTER PROCEDURE [dbo].[Project_Time] 

AS

create table #results
(
    ID varchar(8) null,
    lastname varchar(30) null,
    firstname varchar(30) null,
    rep_time decimal(20,2),
    project_time decimal(20,2) null,
    percent_spent decimal(5,2)
)
insert into #results
select ua.user_id, u.last_name, u.first_name, sum(session_length),
(select sum(session_length) from user_activity ua
where ua.project_id in ('5420')
and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'), null
from user_activity ua
join users u
on u.user_id = ua.user_id
where ua.project_id in ('5420')
and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'
group by ua.user_id, u.last_name, u.first_name

update #results 
set percent_spent = (rep_time/project_time) * 100
from #results

create table #other
(
    ID varchar(8) null,
    lastname varchar(30) null,
    firstname varchar(30) null,
    rep_time decimal(20,2) null,
    project_time decimal(20,2) null,
    percent_spent decimal(5,2)
)
insert into #other
select ua.user_id, u.last_name, u.first_name, sum(session_length), (select sum(session_length)
from user_activity ua
where ua.project_id not in ('5420')
and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'), null
from user_activity ua
join users u
on u.user_id = ua.user_id
where ua.project_id not in ('5420')
and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'
group by ua.user_id, u.last_name, u.first_name

update #other
set percent_spent = (rep_time/project_time) * 100.00
from #other


select r.ID, r.lastname, r.firstname, r.rep_time, r.project_time, r.percent_spent, o.rep_time, o.project_time, o.percent_spent
from #results r
full join #other o
on o.ID = r.ID

Answer 1

您可以从删除更新开始（并用变量替换子查询）：

declare @project_time decimal(20, 2)

select @project_time = sum(session_length) from user_activity ua
where ua.project_id in ('5420') and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'

insert into #results
select ua.user_id, u.last_name, u.first_name, sum(session_length)
, @project_time
, sum(session_length) / @project_time
from user_activity ua
join users u on u.user_id = ua.user_id
where ua.project_id in ('5420') and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'
group by ua.user_id, u.last_name, u.first_name

你也可以用子查询重写整个查询，不用临时 table:

select r.ID, r.lastname, r.firstname, r.rep_time, r.project_time, r.percent_spent, o.rep_time, o.project_time, o.percent_spent
from (
    select ID = ua.user_id, lastname = u.last_name, firstname = u.first_name
        , rep_time = sum(session_length)
        , project_time = @project_time, percent_spent = sum(session_length) / @project_time
    from user_activity ua
    join users u on u.user_id = ua.user_id
    where ua.project_id in ('5420') and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'
    group by ua.user_id, u.last_name, u.first_name
) as r
full join (
    select ID = ua.user_id, lastname = u.last_name, firstname = u.first_name
        , rep_time = sum(session_length)
        , project_time = @project_time, percent_spent = sum(session_length) / @project_time
    from user_activity ua
    join users u on u.user_id = ua.user_id
    where ua.project_id not in ('5420') and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'
    group by ua.user_id, u.last_name, u.first_name
) o
on o.ID = r.ID;

或 CTE：

With result as(
    select ID = ua.user_id, lastname = u.last_name, firstname = u.first_name
        , rep_time = sum(session_length)
        , project_time = @project_time, percent_spent = sum(session_length) / @project_time
    from user_activity ua
    join users u on u.user_id = ua.user_id
    where ua.project_id in ('5420') and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'
    group by ua.user_id, u.last_name, u.first_name
), others as (
    select ID = ua.user_id, lastname = u.last_name, firstname = u.first_name
        , rep_time = sum(session_length)
        , project_time = @project_time, percent_spent = sum(session_length) / @project_time
    from user_activity ua
    join users u on u.user_id = ua.user_id
    where ua.project_id not in ('5420') and session_start_time >= '5/1/15' and session_end_time <= '8/20/15'
    group by ua.user_id, u.last_name, u.first_name
)
select r.ID, r.lastname, r.firstname, r.rep_time, r.project_time, r.percent_spent, o.rep_time, o.project_time, o.percent_spent
from result r
full join others o 
on o.ID = r.ID;

我个人觉得 CTE 版本比子查询或临时 table 版本更容易阅读。然而，这并不意味着它会更好、更快或更慢。

如果你想知道哪个表现更好，你必须逐一研究：

执行计划
IO 使用情况
查询双方涉及的数据量及其变化方式
您的用户 activity table 及其结构的现有（或缺失）索引
...

您还应该从一开始就声明并使用正确的数据类型，而不是在您记住之后再修复它们。不同的数据类型可能给出不同的执行计划。

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