Question

I have a table

id|customer_id|comment
1   34                       good
2   23                       bad
3   34                      regular
4   76                       longterm
5   34                       bad
6   23                      good

We can see that one customer_id has different comment (ex – 34 has good regular bad)
I am trying to pull records from the above table where comment is “good and also bad” and group by customer_id so in the result I should see the records id => 1, 5, 2, 6

Can someone please help me in writing this where clause.

regards

Answer 1

To have one row of data reference another row, you need a join. In this case you’ll want to join comment against itself:

select distinct a.customer_id 
from comments a 
join comments b on a.customer_id = b.customer_id and a.id < b.id 
where a.comment = 'good'
and b.comment = 'bad'

I’ve chosen the a.id < b.id syntax to avoid doing the same join in both directions, resulting in duplicate work. By specifying distinct, you’ll see each customer only once.