比較表中的兩行

Question

作爲作業的一部分，我需要看看在表中兩個給定的講座是否有相同的老師。

表由

lectureNr | nameOfTheLecture | hoursInWeek | professorID 

我做了assingment，原因很複雜，但我只知道做這種方式：

select distinct ( 
     case when 
     (select professorID from vorlesungen where nameOfTheLecture like 'Logik')= 
     (select professorID from vorlesungen where nameOfTheLecture like 'Erkenntnistheorie') 
     then 'yes' else 'no' end) 
from vorlesungen; 

任何人可以sugest我這個美好的solutiuon 。

感謝

Answer 1

select count(distinct professorID) as prof_count 
from vorlesungen 
where nameOfTheLecture in ('Logik','Erkenntnistheorie') 

如果計數大於1那麼他們是不是同一個。

Answer 2

您可以使用ANALYTIC函數ROW_NUMBER。

with data as(
select lectureNr, 
     nameOfTheLecture, 
     hoursInWeek, 
     professorID, 
     row_number() over(partition by professorID order by professorID, nameOfTheLecture) rn 
from vorlesungen 
where nameOfTheLecture in ('Logik','Erkenntnistheorie') 
) 
select * from data 
where rn > 1 
/