Question

我最近被介绍给SQL CTE，我想在这里实现一个，但是我不太确定如何使用我在此查询中的两个不同的表来实现。下面的查询确实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是要走的路，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

您可以先删除更新（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

您还可以使用子查询和临时表重写整个查询：

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;

或使用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;

我个人认为与子查询或临时表版本相比，CTE版本更容易阅读。 Hovewer并不意味着它会更好，更快或更慢。

如果你想知道哪一个会表现更好，你必须研究每一个：

执行计划
IO使用
查询两侧涉及的数据量及其变化方式
用户活动表及其结构上的现有（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，而不是在以后记住它时修复它们。不同的数据类型可以给出不同的执行计划

使用SQL CTE替换多个临时表

1 个答案: