TIL #9: PostgreSQL SQL query to find column count for all the tables in a PostreSQL schema

Today, I wanted to find column count for all the tables in a PostreSQL schema. The following query could be used.

select table_name, count(*) as column_count 
from information_schema."columns" 
where table_schema = 'public'  
GROUP by table_name order by column_count desc;

TIL #8: Installing and Managing PostgreSQL with Brew

This post documents how to install and manage PostgreSQL using brew package manager for macOS.

To install PostgreSQL using brew, run the following command.

$ brew install postgresql

If you wish to start and stop PostgreSQL, then you do that using following brew commands.

$ brew services stop postgresql
$ brew services start postgresql

To get information about your PostgreSQL installation, you can run following brew command.

brew info postgresql

There are time you might forget if you installed PostgreSQL using brew. You can check if PostgreSQL was installed by brew by running following command.

brew list |grep postgres

The brew package manager installs PostgreSQL under following location.


The configuration files as inside following directory.


How to Rename and Change Boolean column to Integer in PostgreSQL

Today, I faced a situation where I had to change a column type from Boolean to Integer. Also, I wanted to rename the column. Let’s suppose, we have tasks table that has a boolean column done. I want to rename done to status and change all false values to 0 and all true values to 1. To do that, you have to run following SQL query using PostgreSQL client.

ALTER TABLE tasks RENAME done TO status;

PostgreSQL learning

To find out the location of PostgreSQL configuration files, just connect with your PostgreSQL database and run the following command.

SELECT name, setting FROM pg_settings WHERE category = 'File Locations';

To describe a table, you should use

\d+ table_name

To list all the databases,you should run following command.


To view all the tables in a schema

\dt+ pg_catalog.pg_t*

To view core settings of a PostgreSQL server, you should use


To view value of a specific setting like effective_cache_size

SHOW effective_cache_size;

To reload the configuration changes

SELECT pg_reload_conf();

To create a new LOGIN user

CREATE ROLE shekhar LOGIN PASSWORD 'p@ssw0rd';

To create a new database


Schema are logical compartments in a database. You can divide your database into small logical schemas.


To view all the available extensions

SELECT * from pg_available_extensions;

To view details about an extension
To view all the available extensions

\dx+ plpgsql;

To install an extension and view its details

postgres=# CREATE EXTENSION fuzzystrmatch;
postgres=# \dx+ fuzzystrmatch;
                    Objects in extension "fuzzystrmatch"
                             Object Description
 function difference(text,text)
 function dmetaphone(text)
 function dmetaphone_alt(text)
 function levenshtein(text,text)
 function levenshtein(text,text,integer,integer,integer)
 function levenshtein_less_equal(text,text,integer)
 function levenshtein_less_equal(text,text,integer,integer,integer,integer)
 function metaphone(text,integer)
 function soundex(text)
 function text_soundex(text)
(10 rows)

To view the active running processes

postgres=# SELECT pid, usename from pg_stat_activity;
 pid  | usename
 1982 | postgres
 2742 | postgres
 2236 | postgres
 2723 | shekhar
 2744 | postgres
(5 rows)

To kill a connection

postgres=# SELECT pg_terminate_backend(2723);
(1 row)

To kill all the connection by user shekhar

SELECT pg_terminate_backend(pid) FROM pg_stat_activity where usename = 'shekhar';

To run a script file, run the following command.

psql -f <path_to_filefile>

You can also run commands with psql non-interactively

psql -d mydb -c "CREATE SCHEMA test;"

The \set command can be used to create user defined shortcuts like as shown below.

\set connections_check 'SELECT pid, usename from pg_stat_activity;'

The .psqlrc file can be used to define configurations for a session. You can use PSQLRC environment variable to control the location of the startup file.

\pset null 'Null'
\encoding latin1
\set PROMPT1 '%n@%M:%>%x %/#'
\set PROMPT2
\timing on
\pset pager always

To turn on timing for the queries execution time


You can call OS shell commands from within psql as shown below.

admin2pnvtk8:myapp#\! env|grep POSTGRES

To view uptime of your PostgreSQL database in minutes, run the following query.

myapp=# select date_trunc('minute',current_timestamp - pg_postmaster_start_time()) as "postgresql_uptime";
(1 row)

How to Host your Java EE Application with Auto-scaling

OpenShift is an auto-scalable Platform as a Service. Auto-scalable means OpenShift can horizontally scale your application up or down depending on the number of concurrent connections. OpenShift supports the JBoss application server, which is a certified platform for Java EE 6 development. As an OpenShift user, you have access to both the community version of JBoss and JBoss EAP 6(JBoss Enterprise Application Platform) for free. In this blog post, we will learn how to host a scalable Java EE 6 application using a JBoss EAP 6 server cluster running on OpenShift. Read the full blog here https://www.openshift.com/blogs/how-to-host-your-java-ee-application-with-auto-scaling

DevFest Austria 2013 Talk : Thinking Beyond RDBMS — Building Polyglot Persistence Java Applications

Couple of weeks back I gave a talk at DevFest Austria event on how to use different nosql datastores with OpenShift.  You can view the video here.