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

Pgpool Configuration & Failback

I would like to share the pgpool configuration, and it's failback mechanism in this post.

Hope it will be helpful to you in creating pgpool and it's failback setup.

Pgpool Installation & Configuration

1. Download the pgpool from below link(Latest version is 3.2.1).
    http://www.pgpool.net/mediawiki/index.php/Downloads


2. Untart the pgpool-II-3.2.1.tar.gz and goto pgpool-II-3.2.1 directory.

3. Install the pgpool by executing the below commands:

./configure ­­prefix=/opt/PostgreSQL92/ ­­--with­-pgsql­-includedir=/opt/PostgreSQL92/include/ --with­-pgsql­-libdir=/opt/PostgreSQL92/lib/ make make install 4. You can see the pgpool files in /opt/PostgreSQL92/bin location.
/opt/PostgreSQL92/bin $ ls clusterdb   droplang  pcp_attach_node  pcp_proc_count pcp_systemdb_info  pg_controldata  pgpool pg_test_fsync pltcl_loadmod  reindexdb createdb    dropuser  pcp_detach_node  pcp_proc_info createlang  ecpg      pcp_node_count   pcp_promote_node oid2name  pcp_pool_status  pcp_stop_pgpool  …

pgBucket - A new concurrent job scheduler

Hi All,

I'm so excited to announce about my first contribution tool for postgresql. I have been working with PostgreSQL from 2011 and I'm really impressed with such a nice database.

I started few projects in last 2 years like pgHawk[A beautiful report generator for Openwatch] , pgOwlt [CUI monitoring. It is still under development, incase you are interested to see what it is, attaching the image here for you ],


pgBucket [Which I'm gonna talk about] and learned a lot and lot about PostgreSQL/Linux internals.

Using pgBucket we can schedule jobs easily and we can also maintain them using it's CLI options. We can update/insert/delete jobs at online. And here is its architecture which gives you a basic idea about how it works.


Yeah, I know there are other good job schedulers available for PostgreSQL. I haven't tested them and not comparing them with this, as I implemented it in my way.
Features are: OS/DB jobsCron style sytaxOnline job modificationsRequired cli options

N-Node Mutlimaster Replication With Bucardo...!

Our team recently got  a problem, which is to solve the N-Node multi master replication in PostgreSQL.

We all know that, there are some other db engines like Postgres-XC which works in this way. But, we don't have any tool available in PostgreSQL, except Bucardo.

Bucardo is the nice solution for 2-Nodes. Is there a way we can exceed this limitation from 2 to N..?

As an initial step on this, I have done with 3 Nodes, which I believe, we can extend this upto N. { I might be wrong here.}

Please follow the below steps to set up the 1 - 1 multi master replication.

1. Follow the below steps to get all the pre-requisites for the Bucardo.

yum install perl-DBIx-Safe or apt-get install libdbix-safe-perl Install the below components from CPAN. DBI DBD::Pg Test::Simple boolean (Bucardo 5.0 and higher) Download the latest tarball from here. tar xvfz Bucardo-4.4.8.tar.gz cd Bucardo-4.4.8 perl Makefile.PL make sudo make install 2. We need to create plperl extension in db. For this, download…