What is the most performant way to rewrite a correlated subquery in the SELECT clause?

Question

I am trying to count whether a user has visited a site in three time ranges:

• last 30 days
• between 31 and 60 days
• between 61 and 90 days

I am using Netezza, which does NOT support correlated subqueries in the SELECT clause. See Rextester for successful query that must be re-written to NOT use a correlated subquery: http://rextester.com/JGR62033

Sample Data:

| user_id | last_visit | num_days_since_2017117 |
|---------|------------|------------------------|
| 1234    | 2017-11-02 | 15.6                   |
| 1234    | 2017-09-30 | 48.6                   |
| 1234    | 2017-09-03 | 75.0                   |
| 1234    | 2017-08-21 | 88.0                   |
| 9876    | 2017-10-03 | 45.0                   |
| 9876    | 2017-07-20 | 120.0                  |
| 5545    | 2017-09-15 | 63.0                   |

Desired Output:

| user_id | last_30 | btwn_31_60 | btwn_61_90 |
|---------|---------|------------|------------|
| 1234    | 1       | 1          | 1          |
| 5545    | 0       | 0          | 1          |
| 9876    | 0       | 1          | 0          |

Answer 1

Here is one way with conditional aggregation, Rextester:

select 
    user_id
    ,MAX(case when '2017-11-17'-visit_date <=30
          then 1
          else 0
     end) as last_30
    ,MAX(case when '2017-11-17'-visit_date >=31
               and '2017-11-17'-visit_date <=60
          then 1
          else 0
     end) as between_31_60
    ,MAX(case when '2017-11-17'-visit_date >=61
              and '2017-11-17'-visit_date <=90
          then 1
          else 0
     end) as between_61_90
from 
    visits
group by user_id
order by user_id