Question

我有3张桌子：

Duties
Activities
Activity Types

一项职责有一项或多项活动，一项活动有多种活动类型。

例如我有2个职责：

值班1有2项活动。活动类型为“TYPE1”的活动1，活动类型为“TYPE2”的活动2。
Duty 2有2项活动，两项活动都有活动类型“TYPE2”。

我希望我的select语句使用“TYPE2”检索所有职责，但如果职责具有活动类型为“TYPE1”，“TYPE2”或任何其他类型的活动，则不应选择它们。即只选择所有活动都有活动类型“TYPE2”的职责。

这是我当前的查询：

select columns from duties d
join activity a on d.duty_id = a.id
join activity_type t on t.id = a.act_id and activity_type = 'TYPE2'

Answer 1

你可以用子查询来支付它，这是可读的方式：＆＃34;所有具有Type2活动的职责，没有其他类型的活动＆＃34; ：

select distinct columns 
from duties d
join activity a2 on d.duty_id = a2.id
join activity_type t2 on t2.id = a2.act_id and activity_type = 'TYPE2'
where d.duty_id not in
( select duty_id.id from duties d
  join activity a on d.duty_id = a.id
  join activity_type t on t.id = a.act_id and activity_type <> 'TYPE2' 
)

请注意，此类查询的性能不高，因为每个主查询行都会执行子查询。

没有标准sql中的子查询：

select columns 
from 
  (
    select columns (including duty_id )
    from duties d
    join activity a on d.duty_id = a.id
    join activity_type t on t.id = a.act_id and activity_type = 'TYPE2'
  ) as yesT2
left outer join
  (
    select distinct d.duty_id 
    from duties d
    join activity a on d.duty_id = a.id
    join activity_type t on t.id = a.act_id and activity_type <> 'TYPE2'
  ) as yesT1
on 
  yesT2.duty_id = yesT1.duty_id
where
  yesT1.duty_id is Null

可读性可提高我们的数据库品牌支持CTE。

Answer 2

select duty_name from duty
except
select duty_name from duties d
join activity a on d.duty_id = a.id
join activity_type t on t.id = a.act_id and activity_type <> 'TYPE2'

这将排除任何具有其他活动类型的活动

从表中只选择一个特定值

2 个答案: