At least one X but no Ys Query

Question

I come across this pattern occasionally and I haven\'t found a terribly satisfactory way to solve it.

Say I have a employee table and an review

Answer 1

Since you haven't posted your DB Structure, I made some assumptions and simplifications (regarding the rating column, which probably is number and not a character field). Adjust accordingly.

Solution 1: Using Joins

select distinct e.EmployeeId, e.Name
from employee e
left join reviews r1 on e.EmployeeId = r1.EmployeeId and r1.rating = 'good'
left join reviews r2 on e.EmployeeId = r2.EmployeeId and r1.rating = 'bad'
where r1.ReviewId is not null --meaning there's at least one
and r2.ReviewId is null --meaning there's no bad review

Solution 2: Grouping By and Filtering with Conditional Count

select e.EmployeeId, max(e.Name) Name
from employee e
left join reviews r on e.EmployeeId = r.EmployeeId
group by e.EmployeeId
having count(case r.rating when 'good' then 1 else null end) > 0
and  count(case r.rating when 'bad' then 1 else null end) = 0

Both solutions are SQL ANSI compatible, which means both work with any RDBMS flavor that fully support SQL ANSI standards (which is true for most RDBMS).

As pointed out by @onedaywhen, the code will not work in MS Access (have not tested, I'm trusting in his expertise on the subject).

But I have one saying on this (which might make some people upset): I hardly consider MS Access a RDBMS. I have worked with it in the past. Once you move on (Oracle, SQL Server, Firebird, PostGreSQL, MySQL, you name it), you do not ever want to come back. Seriously.