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How to get non zero min value from MIN(0, 1, 2)

Hi,

Today, i have faced an interesting problem like below.

I want to get MIN(UNNEST(ARRAY[0, 1, 2, ....]))  as non-zero small element. In this case, it's 1.

Below is my problem description.

postgres=# SELECT SUM(val), MAX(val), MIN(val)
FROM
(
SELECT UNNEST(ARRAY[1, 2, 3]) val
UNION ALL
--Appending some dummy rows, for getting what i would like to expect.
SELECT UNNEST(ARRAY[0, 0, 0]) val
) AS FOO;
 sum | max | min
-----+-----+-----
   6 |  3  | 0
(1 row)

As you see, i can able to identify the sum, max without any problem. But when it comes to "min", i am getting the value as 0. But, I want the minimum as 1 as per my requirement. I can able to get the min, max, sum from the first array it self. But, my implementation doesn't allow this. :(

I have tried it in so many ways, and finally found the following solution. I believe, there will be some better ways also, but just wanted to keep a note on this.

postgres=# SELECT SUM(val), MAX(val), 
COALESCE((SELECT * FROM UNNEST(array_agg(val)) WHERE unnest!=0 ORDER BY unnest ASC LIMIT 1), 0) AS min
postgres-# FROM
postgres-# (
postgres(# SELECT UNNEST(ARRAY[1, 2, 3]) val
postgres(# UNION ALL
postgres(# SELECT UNNEST(ARRAY[0, 0, 0]) val
postgres(# ) AS FOO;
 sum | max | min 
-----+-----+-----
   6 |   3 |   1

(1 row)

Hope it helps to someone.


Dinesh Kumar

Comments

  1. Just add WHERE val > 0:

    SELECT SUM(val), MAX(val), MIN(val)
    FROM
    (
    SELECT UNNEST(ARRAY[1, 2, 3]) val
    UNION ALL
    SELECT UNNEST(ARRAY[0, 0, 0]) val
    ) AS FOO
    WHERE val > 0;

    ReplyDelete
    Replies
    1. Thank you for the answer. Yes, it's the way we can also do. But in the case of the first array , if it's like ARRAY[0, 0, 0] then i don't get any rows. I could post this along with my full requirement. I am really sorry for the partial details.

      Delete
  2. You can also use MIN(CASE WHEN val = 0 THEN NULL ELSE val END)

    ReplyDelete
    Replies
    1. Thank you very much paul. Yes, it defiantly do the same thing. In the case of 1st ARRAY[0, 0, 0] i will get the min as null, where i was expecting to give 0. I am really sorry to post this blog with partial details. I will try to give full details, when i do next time.

      Delete
    2. I like the 9.4 filter feature otherwise this I like best combined with a coalesce to provide your zero if no non-zero values are present. This is explicit about not evaluating zero while the nullif is maybe shorter but, to me at least, a very non-typical use of that function.

      Delete
  3. The following should work as well. MIN(NULLIF(val,0))

    ReplyDelete
    Replies
    1. Thanks for your inputs. i believe this don't work with ARRAY[0, 0, 0]. I am really really sorry to post blog with partial details. Anyhow, thank you very much for your time.

      Delete
    2. Same anonymous poster. COALESCE(MIN(NULLIF(val,0)),0)

      Delete
    3. Ah. Yes this one. Thank you very much.

      Delete
  4. PostgreSQL 9.4: coalesce(min(val) filter (where val > 0), 0)

    ReplyDelete

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