Question

The inner query here returns values that only appear in one of the tables. The outer query is supposed to return a count of those. Instead, it returns the entire table, not just the NULL values.

select count(*) from tblicd
where exists
(
select i.icd_id
from tblicd i left outer join icd_jxn on icd_jxn.icd_id=i.icd_id
where icd_jxn.icd_id is null
)

The inner query

select i.icd_id
    from tblicd i left outer join icd_jxn on icd_jxn.icd_id=i.icd_id
    where icd_jxn.icd_id is null

works and does what I want. I’d like (using a sub query method like this) to use the outer query to just return the number of rows that the inner query returns.

Answer 1

You need to join the two (outer and inner) tblicd tables in the subquery:

and i.icd_id = tblicd.icd_id

(or whatever the id of the tblicd table is)