从左表获取所有记录，并计算列值

Question

I have master table with structure :

T1

ID    Name
1     Cricket
2     Football
3     Golf

T2

ID    T1-ID    SomeNumber
1     1        180
2     2        180
3     1        195
4     3        195

Column T1-ID is foreign ket fot table T1, ID column. I want to get resultset for value in Somenumber for '180' like

Output :

ID    Name        ComputedColumn
1     Cricket     True
2     Football    True
3     Golf        False

I have tried using Left-Joins, Case Statements but didnt get expected results.

Answer 1

You can use left join :

select t1.*,
       (case when t2.id is null then 'False' else 'True' end) as ComputedColumn
from t1 left join
     t2
     on t1.id = t2.t1_id and t2.somenumber = 180;

Actually, that assumes that a row with 180 occurs at most once for each id (as in your sample data). If such rows could occur multiple times, use case :

select t1.*,
       (case when exists (select 1 from t2 where t1.id = t2.t1_id and t2.somenumber = 180)
             then 'True' else 'False'
        end) as ComputedColumn
from t1;