Skip to main content

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

Post a Comment

Popular posts from this blog

Parallel Operations With pl/pgSQL

Hi, I am pretty sure that, there will be a right heading for this post. For now, i am going with this. If you could suggest me proper heading, i will update it :-) OK. let me explain the situation. Then will let you know what i am trying to do here, and how i did it. Situation here is, We have a table, which we need to run update on “R” no.of records. The update query is using some joins to get the desired result, and do update the table.  To process these “R” no.of records, it is taking “H” no.of hours. That too, it’s giving load on the production server. So, we planned to run this UPDATE as batch process.  Per a batch process, we took “N” no.or records. To process this batch UPDATE, it is taking “S” no.of seconds. With the above batch process, production server is pretty stable, and doing great. So, we planned to run these Batch updates parallel.  I mean, “K” sessions, running different record UPDATEs. Of-course, we can also increase the Batch size here.  But

How To Send E-Mail From PostgreSQL

Hi , If you want to send E-Mails from PostgreSQL, then use the below Python 3.2 Script as below. I have used ActivePython 3.2 with PostgreSQL 9.1 for sending E-Mails from PostgreSQL. If you want to configure the Python 3.2 with PostgreSQL 9.1 then, please refer the below steps. http://manojadinesh.blogspot.in/2012/06/fatal-python-error-pyinitialize-unable.html Once, your Python 3.2 successful then follow the below steps to send an e-mail. Step 1 ===== postgres=# CREATE OR REPLACE FUNCTION public.send_email(_from Text,_password Text,smtp Text,port INT,receiver text, subject text, send_message text) RETURNS TEXT  LANGUAGE plpython3u AS $function$ import smtplib sender = _from receivers = receiver message = ("From: %s\nTo: %s\nSubject: %s\n\n %s"  % (_from,receiver,subject,send_message)) try:   smtpObj = smtplib.SMTP(smtp,port)   smtpObj.starttls()   smtpObj.login(_from, _password)   smtpObj.sendmail(sender, receivers,message)   print ('Successf

::Pipelined in Oracle as well in PostgreSQL::

Pipelined Table Functions:- [ORACLE] =========================== If you want to return multiple rows to the calling environment, then piplined table functions is prefred. It will increase the dbperformance as well. Ex:- Step 1: ----------- CREATE TABLE EMP(EMPNO INT,ENAME VARCHAR2(10),SAL INT); Step 2: ----------- Insert sample data. Step 3: ----------- Create an object for the row type casting. CREATE OR REPLACE TYPE emp_row AS OBJECT ( empno INT, ename VARCHAR2(20), SAL INT ); Step 4: ----------- Create a Return Type for the pipelined function. CREATE OR REPLACE TYPE emp_table_type AS TABLE OF emp_row; Step 5: ----------- CREATE OR REPLACE FUNCTION emp_pipe_function RETURN emp_table_type PIPELINED IS BEGIN FOR rec in (select * from emp) LOOP PIPE ROW (emp_row(rec.empno,rec.ename,rec.sal)); END LOOP; RETURN; END; Step 6: ---------- SQL> select * from table(emp_pipe_function); EMPNO ENAME SAL ---------- ----