CODEWITHSUNDEEP
sqlvertica
Polly
Polly

Reputation: 1097

JOIN on range between current and previous row

could anyone help me please? I have two tables: Prices and Intervals:

   Prices:           Intervals:
   Price         Interval_bound  Category
    16                 5         cheap
    11                 10        cheap
    9                  15        median
    26                 20        median
    6                  25        expensive

I need to join the Category values to the Price according to their interval, where Interval_bound is the lowest bound of category:

Price  Category
 16      median
 11      cheap
 9       cheap
 26      expensive
 6       cheap

I've tried to do it with

select Price, Category from Prices 
left join Intervals on Prices.Price interpolate previous value Interval.Interval_bound

but it gives me only NULL for Category. How can I do it the easiest way? I'm using Vertica.

Upvotes: 3

Views: 320

Answers (2)

marcothesane
marcothesane

Reputation: 6749

I'm puzzled - why would your version not work?

-- your input ..
WITH
prices(price) AS (
          SELECT 16
UNION ALL SELECT 11
UNION ALL SELECT  9
UNION ALL SELECT 26
UNION ALL SELECT  6
)
, 
-- your other input 
intervals(interval_bound,category) AS (
          SELECT  5,'cheap'
UNION ALL SELECT 10,'cheap'
UNION ALL SELECT 15,'median'
UNION ALL SELECT 20,'median'
UNION ALL SELECT 25,'expensive'
)
-- the way I would write it ...
SELECT
  p.price
, i.category
FROM prices p
LEFT JOIN intervals i
ON p.price INTERPOLATE PREVIOUS VALUE i.interval_bound
;
 price | category
-------+-----------
     6 | cheap
     9 | cheap
    11 | cheap
    16 | median
    26 | expensive

-- the way you wrote it ...
select Price, Category from Prices
left join Intervals on Prices.Price interpolate previous value Intervals.Interval_bound;
 Price | Category
-------+-----------
     6 | cheap
     9 | cheap
    11 | cheap
    16 | median
    26 | expensive

What went wrong in your case?

Upvotes: 1

Gordon Linoff
Gordon Linoff

Reputation: 1270773

You can use lead() to get the next upper bound and then join:

select p.Price, i.Category
from Prices p left join
     (select i.*,
             lead(interval_bound) over (order by interval_bound) as next_interval_bound
      from Intervals i
     ) i
     on p.price >= i.interval_bound and
        (p.price < i.next_interval_bound or i.next_interval_bound is null);

Upvotes: 3

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