How to get the proper SQL result from a query

Question

I have a view in my database that uses several tables and everything works fine the way it is now. I want to add another column/value based on whether a specific match is found in another table. I have used similar iterations in others, but this time I get a NULL result, even though there is a match.

Basically:

Table_2

ID	Value	Text
1	Miss	Some text
1	Miss	Other text
2	Hit	OK
2	Miss	Always
3	Hit	Whatelse

There is a correlation to another table that holds a value, equal to the ID in Table_2.

I want to use a case when and set a text based on this;

select 
    somefield1,
    somefield2,
    somefield3,
    case
        when 2.ID is not null then 'Real'
        else 'Fake'
    end somefield4
from
    table_1 1 (nolock)
left join 
    (select top (1) ID from table_2 where Value = 'Hit') 2 on 1.ID = 2.ID

If I run this script:

select top (1) ID 
from table_2 
where Value = 'Hit' and ID = 2

it returns: 2

If I run this:

select top (1) ID 
from table_2 
where Value = 'Hit' and ID = 1

it returns: NULL

But when I run the view, I get 'Fake' every single time, even though there is a match and the query returns a value.

Answer 1

If I understand correctly, you can use exists to check if the appropriate row exists in the other table. This looks like:

select t2.*,
       (case when exists (select 1
                          from table_1 t1
                          where t1.id = t2.id and t1.event = 'Hit'
                         )
             then 'real' else 'fake'
        end)
from table_2 t2;

For performance, you want an index on table_1(id, event) .