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PostgreSQL

$ sudo -u postgres dropdb development_app
$ sudo -u postgres createdb development_app
$ sudo -u postgres pg_restore  --dbname=development_app  dump.dump 

debug postgres huge cpu usage

SELECT * FROM pg_stat_activity;

once you find proces causing issue (usually one stuck there active for hours) kill it

  # SELECT pg_cancel_backend(pid-of-the-postgres-process);   # 3rd line of pg_stat_activity;
  SELECT pg_cancel_backend(123456);  

in docker container

psql --username="$DB_ENV_POSTGRES_USERNAME" --host="$DB_PORT_5432_TCP_ADDR" --dbname="$DB_ENV_POSTGRES_DATABASE" -c 'SELECT * from pg_stat_activity ;'  --password >> /tmp/out.txt

Rails time gt date lt

MyModel.where('"created_at" > ?', Time.new(2015).to_s(:db))

clusters and upgrading postgres

command that will give you information on existing clusters

sudo pg_lsclusters

upgrade from 9.1 to 9.3

sudo pg_lsclusters
sudo pg_dropcluster --stop 9.3 main #  delete the default 9.3 cluster created by the 9.3 install.
sudo pg_upgradecluster 9.1 main     #  create a new 9.3 cluster from the existing 9.1 cluster
sudo service postgresql start 9.3
sudo pg_dropcluster --stop 9.1 main      # delete the 9.1 Cluster.

array

to create rails migration for array (it can be text as well as postgres will make it array)

http://www.postgresql.org/docs/9.1/static/arrays.html

  create_table "email_logs" do |t|
    t.integer  "user_tld_id"
    t.string   "category",       default: [], array: true
  end

array search

SELECT  "email_logs".* FROM "email_logs" WHERE user_tld_id = 3 AND 'reminder' = ANY (category) LIMIT 1;

Functions

CREATE FUNCTION add_em(integer, integer) RETURNS integer AS $$
    SELECT $1 + $2;
$$ LANGUAGE SQL;

SELECT add_em(1, 2) AS answer;


CREATE FUNCTION domain_count(text) RETURNS bigint AS $$
  SELECT COUNT(*) FROM "applications" WHERE "applications"."domain" = $1;
$$ LANGUAGE SQL;

SELECT domain_count('developer-test.com') AS domain_count;

export query to csv

Copy (Select * From foo) To '/tmp/test.csv' With CSV;

source: http://stackoverflow.com/questions/1517635/save-postgres-sql-output-to-csv-file

duplicate

# what domains are duplicated
SELECT domain FROM applications GROUP BY domain HAVING COUNT(domain) > 1;

   domain   
------------
 joe.com    
 zoe.com    


# therefore 
select * from applications where domain in (SELECT domain FROM applications GROUP BY domain HAVING COUNT(domain) > 1);


# select every column of fields that are duplicated BUT ONLY ONE OF EACH
# solution look nice but you may face several issues
#
SELECT * FROM (select * ROW_NUMBER() OVER(PARTITION BY domain) AS domain_count FROM applications) dups WHERE dups.domain_count > 1;
   domain   | domain_count  |
------------+-------------- |
 joe.com    |            3  |
 zoe.com    |            2  |

general notes

postgress -D /var/local/var/pg_db -! /tmp/pglog # -D specify  vher db is saved, -l where log is  saved
psql
  \d  #list databases
  \d  my_db  #list tables of db 
  \d  table  #list colums
  \l    #list all databases
  
  \du # list all users
  

mysql:  use database_name;
postgres: \c database_name;
    
mysql: SHOW TABLES
postgresql: \d
postgresql: SELECT table_name FROM information_schema.tables WHERE table_schema = 'public';

mysql: SHOW DATABASES
postgresql: \l
postgresql: SELECT datname FROM pg_database;

mysql: SHOW COLUMNS
postgresql: \d table
postgresql: SELECT column_name FROM information_schema.columns WHERE table_name ='table';

mysql: DESCRIBE TABLE
postgresql: \d+ table
postgresql: SELECT column_name FROM information_schema.columns WHERE table_name ='table';


rails new --database=postgres
gem 'pg'
1255

Dump

Load dump

 sudo -u postgres psql db_name < dump.db 

in heroku


pg_restore --verbose --clean --no-acl --no-owner -h localhost -U myuser -d mydb latest.dump
# ..or
 sudo -upostgres pg_restore --verbose --clean --no-acl --no-owner -d mydb latest.dump

pg_dump for pg_restore the dump must be in tar format so e.g. pg_dump --format=t

create dump

pg_dump db_name > dump.db

http://www.postgresql.org/docs/9.1/static/backup-dump.html

create database & user & change root password

  CREATE USER tom WITH PASSWORD 'myPassword';
  CREATE DATABASE jerry;
  GRANT ALL PRIVILEGES ON DATABASE jerry to tom;
  
  ALTER USER postgres WITH PASSWORD 'happyface';
  
  \du  # list all users
  DROP USER username;  #you need to change owner of databases first
  
  # change owner of database
  ALTER DATABASE name OWNER TO new_owner;
  
  # rename user 
  ALTER USER name RENAME TO newname;

higher changes with user in Postgress

  ALTER USER myuser WITH SUPERUSER; # will be superuser
  ALTER USER myuser WITH CREATEDB;  # can create db

http://www.postgresql.org/docs/current/static/sql-alterdatabase.html

fedora start postgress

  psql --username=postgres

Install postgresql 9.3 on Ubuntu 14.04

sudo apt-get update
sudo apt-get install postgresql-9.3 libpq-dev

#check instalation
locate postgresql
psql -V

for Ubuntu 12.04 & postgres 9.1 check http://railskey.wordpress.com/2012/05/19/postgresql-installation-in-ubuntu-12-04/

mint & ubuntu postgres

sudo -u postgres psql 

# be sure to include host=localhost in config/database.yml with ubuntu

# How to start / stop the server?
sudo service postgresql start / stop
sudo /etc/init.d/postgresql start / stop

mac OSx postgres console

sudo -u tomi psql postgres    # tomi represent system user

source: https://zxmax.wordpress.com/2012/05/26/install-postgers-9-3-on-ubuntu-12-04/

mint ubuntu start login to postgress

 sudo -u postgres psql  # login from root
 
 psql -d postgres -U postgres --password --host=localhost

add hstore to database

sudo -u postgres psql my_app_development

create extension hstore;

if you get PG::Error: ERROR: could not open extension control file "/usr/share/postgresql/9.1/extension/hstore.control": No such file or directory : CREATE EXTENSION IF NOT EXISTS hstore run:

sudo apt-get install postgresql-contrib

source http://stackoverflow.com/questions/19467481/postgres-hstore-exists-and-doesnt-exist-at-same-time

postgres hstore queries

Product.create(properties: {rating: 'PG-13', runtime: '103'} )

Product.where("properties -> 'rating' = 'PG-13'")
Product.where("properties -> 'rating' LIKE '%G%'")
Product.where("(properties -> 'rating')::int > 100")

Rails Hstore object has different Object ID each time you call it, so you cannot do this:

foo.properties['rating'] = '123' # wont save
foo.properties # => {}

...you need to set the full properties hash each time

foo.properties  { rating: 'foo'}

...so to do setra method you need to have

def author=(value)
  self.properties = (properties || {}).merge(author: value)
end

sources:

  • railscasts-345

moving postgres datastore location

sudo su postgres
psql
>    SHOW data_directory;

let say /var/lib/postgresql/9.3/main/postgresql.conf

mkdir -p /mnt/database_volume/postgres
chown -R postgres:postgres /mnt/database_volume/postgres

/usr/lib/postgresql/9.1/bin/initdb -D /mnt/database_volume/postgres # this will init the dir structure

now vim /etc/postgresql/9.3/main/postgresql.conf

... and change:

data_directory = '/var/lib/postgresql/9.3/main/'

... to:

data_directory = '/mnt/database_volume/postgres/'

Now kill postgress (killall -9 postgre)

... and start it sudo /etc/init.d/postgresql restart

If you need to remove system autostart (e.g. your /mnt/database_volume is encrypted) you can do it by remonig rc-d

sudo update-rc.d -f postgresql remove`

source:

pure Postgres JSON API

http://blog.redpanthers.co/create-json-response-using-postgresql-instead-rails/

select row_to_json(users) from users where id = 1;
{"id":1,"email":"hsps@redpanthers.co","encrypted_password":"iwillbecrazytodisplaythat",
"reset_password_token":null,"reset_password_sent_at":null,
"remember_created_at":"2016-11-06T08:39:47.983222",
"sign_in_count":11,"current_sign_in_at":"2016-11-18T11:47:01.946542",
"last_sign_in_at":"2016-11-16T20:46:31.110257",
"current_sign_in_ip":"::1","last_sign_in_ip":"::1",
"created_at":"2016-11-06T08:38:46.193417",
"updated_at":"2016-11-18T11:47:01.956152",
"first_name":"Super","last_name":"Admin","role":3}

specific fields:

select row_to_json(results)
from (
  select id, email from users
) as results
{"id":1,"email":"hsps@redpanthers.co"}

more advanced

select row_to_json(result)
from (
  select id, email,
    (
      select array_to_json(array_agg(row_to_json(user_projects)))
      from (
        select id, name
        from projects
        where user_id=users.id
        order by created_at asc
      ) user_projects
    ) as projects
  from users
  where id = 1
) result
{"id":1,"email":"hsps@redpanthers.co", "project":["id": 3, "name":"CSnipp"]}
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