How To Install and Use PostgreSQL on Ubuntu 12.04
Install PostgresBefore we install postgres, we should quick perform a quick update of the apt-get repository:
apt-get updateOnce apt-get has updated go ahead and download Postgres and its helpful accompanying dependencies:
sudo apt-get install postgresql postgresql-contribWith that, postgres is installed on your server.
Create Your PostgreSQL Roles and DatabasesOnce Postgres has been installed on your server, you can start to configure the database.
Postgres uses the concept of roles to distinguish the variety of users that can connect to a database. When it is first installed on a server, the default postgres user is actual named "postgres”. The other users are specified in one of variety of ways. The common methods are ident and md5.
The postgres default is to use ident authentication, tying each server user to a Postgres account. The alternative which can be set in the authentication configuration, located in "/etc/postgresql/9.1/main/pg_hba.conf " is md5 which asks the client to supply an encrypted password. To begin creating custom users, first switch into the default user:
su – postgresOnce logged in as this user, you can move forward to create more roles in your PostgreSQL system:
Enter name of role to add: newuser Shall the new role be a superuser? (y/n) yTo outfit your user with a password, you can add the words –pwprompt to the createuser command:
Connecting to the Postgres DatabasesWith the users that you want to use to log into your Postgres shell set up, you can proceed to make a database for them to use. You can create the Postgres database as a superuser. In this case, we will use the default super user. Go ahead and switch into the postgres user once again:
su – postgresAs postgres, you can start to create your first usable postgres database:
createdb eventsAnd with that you can finally connect to the postgres shell.
How to Create and Delete a Postgres TablesOnce we log into the correct database (using the
Let’s imagine that we are planning a get together of friends. We can use Postgres to track the details of the event.
Let’s create a new Postgres table:
CREATE TABLE potluck (name VARCHAR(20), food VARCHAR(30), confirmed CHAR(1), signup_date DATE);This command accomplishes a number of things:
CREATE TABLEYou can additionally see all of the tables within the database with the following command:
\dtThe result, in this case, should look like this:
postgres=# \dt List of relations Schema | Name | Type | Owner --------+---------+-------+------- public | potluck | table | root (1 row)
How to Add Information to a Postgres TableWe have a working table for our party. Now it’s time to start filling in the details.
Use this format to insert information into each row:
INSERT INTO potluck (name, food, confirmed, signup_date) VALUES('John', 'Casserole', 'Y', '2012-04-11');Once you input that in, you will see the words:
INSERT 0 1Let’s add a couple more people to our group:
INSERT INTO potluck (name, food, confirmed, signup_date) VALUES('Sandy', 'Key Lime Tarts', 'N', '2012-04-14'); INSERT INTO potluck (name, food, confirmed, signup_date)VALUES ('Tom', 'BBQ','Y', '2012-04-18'); INSERT INTO potluck (name, food, confirmed, signup_date) VALUES('Tina', 'Salad', 'Y','2012-04-18');We can take a look at our table:
SELECT * FROM potluck; name | food | confirmed | signup_date -------+----------------+-----------+------------- John | Casserole | Y | 2012-04-11 Sandy | Key Lime Tarts | N | 2012-04-14 Tom | BBQ | Y | 2012-04-10 Tina | Salad | Y | 2012-04-18 (4 rows)Should we want to, then, follow up by removing an unlucky attendee, in this John and his casserole, from our potluck we can accomplish this with the Delete command:
DELETE FROM potluck WHERE name = 'John' ;
How to Add and Delete a ColumnWe are creating a handy chart, but it is missing some important information: our attendees’ emails. We can easily add this:
ALTER TABLE potluck ADD email VARCHAR(40);This command puts the new column called "email" at the end of the table by default, and the VARCHAR command limits it to 40 characters. Just as you can add a column, you can delete one as well:
ALTER TABLE potluck DROP email;I guess we will never know how to reach the picnickers.
How to Update Information in the TableNow that we have started our potluck list, we can address any possible changes. For example: Sandy has confirmed that she is attending, so we are going to update that in the table.
UPDATE potluck set confirmed = 'Y' WHERE name = 'Sandy';You can also use this command to add information into specific cells, even if they are empty.
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