Question

I am trying to fetch records from 2 tables mapped by an id where on the second table there may be a row that is missing.

I have a column called name on the second table which contains a string value. The value I need to extract is ‘subscriptions’ but this does not always exist in the table. There is the possibility to have different values within this column which I do not want to extract.

Is it possible to check to see if the value exists and if it doesn’t output null to all the fields.

So far I have this which returns all the records

select COUNT(*) 
from PUser a, PAttribute b
where exists (select null 
              from PAttribute c 
              where c.name = 'subscriptions' or c.name is null) 
   and a.id = b.userid;

Hope that explains it.

EDIT

PUser table

id
other columns

PAttribute table

userid mapped to PUser.id
name

Now a userid can have multiple rows each with a different value in name eg, ‘subscriptions’, ‘source’, ‘etc’ ‘etc’

I want to fetch all users who have the value ‘subscriptions’ in the name column or if the row doesnt exist with the value ‘subscriptions’ as they may not have any.

If they don’t have this row the output should be null.

EDIT 2:

Worked this out and I needed

select COUNT(*),(select b.stringValue from PAttribute b where b.userid = a.id and b.name = 'subscriptions') from PUser a order by a.id desc;

Answer 1

Your example is using implicit joins, which are inner joins. This means that a result will only be returned if a row exists in both tables. Instead, you need to use a left join. Change your query to this:

select COUNT(*)  
from PUser a LEFT JOIN PAttribute b ON a.id = b.userID
where exists (select null  
              from PAttribute c  
              where c.name = 'subscriptions' or c.name is null);

Or (not exactly sure what your desired behavior is), this might work for you:

SELECT count(*)
FROM PUser a LEFT JOIN PAttribute b ON a.id = b.userID
WHERE b.name = 'subscriptions' OR b.name IS NULL;