A Basic MySQL Tutorial

About MySQL

MySQL is an open source database management software that helps users store, organize, and retrieve data. It is a very powerful program with a lot of flexibility—this tutorial will provide the simplest introduction to MySQL

How to Install MySQL on Ubuntu and CentOS

If you don't have MySQL installed on your droplet, you can quickly download it.

Ubuntu:

sudo apt-get install mysql-server

Centos:

sudo yum install mysql-server
/etc/init.d/mysqld start

How to Access the MySQL shell

Once you have MySQL installed on your droplet, you can access the MySQL shell by typing the following command into terminal:

mysql -u root -p

After entering the root MySQL password into the prompt (not to be confused with the root droplet password), you will be able to start building your MySQL database.

Two points to keep in mind:

• All MySQL commands end with a semicolon; if the phrase does not end with a semicolon, the command will not execute.
• Also, although it is not required, MySQL commands are usually written in uppercase and databases, tables, usernames, or text are in lowercase to make them easier to distinguish. However, the MySQL command line is not case sensitive.

How to Create and Delete a MySQL Database

MySQL organizes its information into databases; each one can hold tables with specific data.

You can quickly check what databases are available by typing:

SHOW DATABASES;

Your screen should look something like this:

 mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+
4 rows in set (0.01 sec)

Creating a database is very easy:

 CREATE DATABASE database name;

In this case, for example, we will call our database "events."

 mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| events             |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)

In MySQL, the phrase most often used to delete objects is Drop. You would delete a MySQL database with this command:

 DROP DATABASE database name;

How to Access a MySQL Database

Once we have a new database, we can begin to fill it with information.

The first step is to create a new table within the larger database.

Let’s open up the database we want to use:

 USE events;

In the same way that you could check the available databases, you can also see an overview of the tables that the database contains.

 SHOW tables; 

Since this is a new database, MySQL has nothing to show, and you will get a message that says, “Empty set”

How to Create a MySQL Table

Let’s imagine that we are planning a get together of friends. We can use MySQL to track the details of the event.

Let’s create a new MySQL table:

CREATE TABLE potluck (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, 
name VARCHAR(20),
food VARCHAR(30),
confirmed CHAR(1), 
signup_date DATE);

This command accomplishes a number of things:

1. It has created a table called potluck within the directory, events.
2. We have set up 5 columns in the table—id, name, food, confirmed, and signup date.
3. The “id” column has a command (INT NOT NULL PRIMARY KEY AUTO_INCREMENT) that automatically numbers each row.
4. The “name” column has been limited by the VARCHAR command to be under 20 characters long.
5. The “food” column designates the food each person will bring. The VARCHAR limits text to be under 30 characters.
6. The “confirmed” column records whether the person has RSVP’d with one letter, Y or N.
7. The “date” column will show when they signed up for the event. MySQL requires that dates be written as yyyy-mm-dd

Let’s take a look at how the table appears within the database using the "SHOW TABLES;" command:

 mysql> SHOW TABLES;
+------------------+
| Tables_in_events |
+------------------+
| potluck          |
+------------------+
1 row in set (0.01 sec)

We can remind ourselves about the table’s organization with this command:

 DESCRIBE potluck;

Keep in mind throughout that, although the MySQL command line does not pay attention to cases, the table and database names are case sensitive: potluck is not the same as POTLUCK or Potluck.

 mysql>DESCRIBE potluck;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| id          | int(11)     | NO   | PRI | NULL    | auto_increment |
| name        | varchar(20) | YES  |     | NULL    |                |
| food        | varchar(30) | YES  |     | NULL    |                |
| confirmed   | char(1)     | YES  |     | NULL    |                |
| signup_date | date        | YES  |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)

How to Add Information to a MySQL Table

We 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` (`id`,`name`,`food`,`confirmed`,`signup_date`) VALUES (NULL, "John", "Casserole","Y", '2012-04-11');

Once you input that in, you will see the words:

 Query OK, 1 row affected (0.00 sec)

Let’s add a couple more people to our group:

INSERT INTO `potluck` (`id`,`name`,`food`,`confirmed`,`signup_date`) VALUES (NULL, "Sandy", "Key Lime Tarts","N", '2012-04-14');
INSERT INTO `potluck` (`id`,`name`,`food`,`confirmed`,`signup_date`) VALUES (NULL, "Tom", "BBQ","Y", '2012-04-18');
INSERT INTO `potluck` (`id`,`name`,`food`,`confirmed`,`signup_date`) VALUES (NULL, "Tina", "Salad","Y", '2012-04-10'); 

We can take a look at our table:

mysql> SELECT * FROM potluck;
+----+-------+----------------+-----------+-------------+
| id | name  | food           | confirmed | signup_date |
+----+-------+----------------+-----------+-------------+
|  1 | John  | Casserole      | Y         | 2012-04-11  |
|  2 | Sandy | Key Lime Tarts | N         | 2012-04-14  |
|  3 | Tom   | BBQ            | Y         | 2012-04-18  |
|  4 | Tina  | Salad          | Y         | 2012-04-10  |
+----+-------+----------------+-----------+-------------+
4 rows in set (0.00 sec)

How to Update Information in the Table

Now 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 `potluck`.`name` ='Sandy';

You can also use this command to add information into specific cells, even if they are empty.

How to Add and Delete a Column

We 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.

However, if you need to place that column in a specific spot in the table, we can add one more phrase to the command.

 ALTER TABLE potluck ADD email VARCHAR(40) AFTER name; 

Now the new “email” column goes after the column “name”.

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 Delete a Row

If needed, you can also delete rows from the table with the following command:

DELETE from [table name] where [column name]=[field text];

For example, if Sandy suddenly realized that she will not be able to participate in the potluck after all, we could quickly eliminate her details.

mysql> DELETE from potluck  where name='Sandy';
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM potluck;
+----+------+-----------+-----------+-------------+
| id | name | food      | confirmed | signup_date |
+----+------+-----------+-----------+-------------+
|  1 | John | Casserole | Y         | 2012-04-11  |
|  3 | Tom  | BBQ       | Y         | 2012-04-18  |
|  4 | Tina | Salad     | Y         | 2012-04-10  |
+----+------+-----------+-----------+-------------+
3 rows in set (0.00 sec)

How To Create a New User and Grant Permissions in MySQL

What the Red Means

The lines that the user needs to enter or customize will be in red in this tutorial! The rest should mostly be copy-and-pastable.

About MySQL

MySQL is an open source database management software that helps users store, organize, and later retrieve data. It has a variety of options to grant specific users nuanced permissions within the tables and databases—this tutorial will give a short overview of a few of the many options.

How to Create a New User

In Part 1 of the MySQL Tutorial, we did all of the editing in MySQL as the root user, with full access to all of the databases. However, in the cases where more restrictions may be required, there are ways to create users with custom permissions.

Let’s start by making a new user within the MySQL shell:

CREATE USER 'newuser'@'localhost' IDENTIFIED BY 'password';

Sadly, at this point newuser has no permissions to do anything with the databases. In fact, if newuser even tries to login (with the password, password), they will not be able to reach the MySQL shell.

Therefore, the first thing to do is to provide the user with access to the information they will need.

GRANT ALL PRIVILEGES ON * . * TO 'newuser'@'localhost';

The asterisks in this command refer to the database and table (respectively) that they can access—this specific command allows to the user to read, edit, execute and perform all tasks across all the databases and tables.

Once you have finalized the permissions that you want to set up for your new users, always be sure to reload all the privileges.

FLUSH PRIVILEGES;

Your changes will now be in effect.

How To Grant Different User Permissions

Here is a short list of other common possible permissions that users can enjoy.

• ALL PRIVILEGES- as we saw previously, this would allow a MySQL user all access to a designated database (or if no database is selected, across the system)
• CREATE- allows them to create new tables or databases
• DROP- allows them to them to delete tables or databases
• DELETE- allows them to delete rows from tables
• INSERT- allows them to insert rows into tables
• SELECT- allows them to use the Select command to read through databases
• UPDATE- allow them to update table rows
• GRANT OPTION- allows them to grant or remove other users' privileges

To provide a specific user with a permission, you can use this framework:

 GRANT [type of permission] ON [database name].[table name] TO ‘[username]’@'localhost’;

If you want to give them access to any database or to any table, make sure to put an asterisk (*) in the place of the database name or table name.

Each time you update or change a permission be sure to use the Flush Privileges command.

If you need to revoke a permission, the structure is almost identical to granting it:

 REVOKE [type of permission] ON [database name].[table name] FROM ‘[username]’@‘localhost’;

Just as you can delete databases with DROP, you can use DROP to delete a user altogether:

 DROP USER ‘demo’@‘localhost’;

To test out your new user, log out by typing

 quit 

and log back in with this command in terminal:

mysql -u [username]-p

How to Import and Export Databases

Export

To Export a database, open up terminal, making sure that you are not logged into MySQL and type,
mysqldump -u [username] -p [database name] > [database name].sql

The database that you selected in the command will now be exported to your droplet.

Import

To import a database, first create a new blank database in the MySQL shell to serve as a destination for your data.
CREATE DATABASE newdatabase;

Then log out of the MySQL shell and type the following on the command line:
mysql -u [username] -p newdatabase < [database name].sql

With that, your chosen database has been imported into your destination database in MySQL.



How to Reset a Root Password

When you first install MySQL, you have to set up your root password. However, should you forget it at any point, you can still recover it.

Step One—Shut Down MySQL

In terminal, stop the MySQL process
 /etc/init.d/mysql stop

Step Two—Access MySQL Safe Mode

In safe mode, you will be able to make changes within the MySQL system with a root password alone, without the need for MySQL root password.
sudo mysqld_safe --skip-grant-tables &

Once safe mode has started up, log into MySQL and when prompted, use your standard root password.
mysql -u root mysql

Step Three—Set Up a New Password

Finally, set up the new MySQL root password by typing the command below. Replace "newpassword" with the password of your choice.
update user set password=PASSWORD("newpassword") where User='root';

Be sure to reload everything:
 FLUSH PRIVILEGES;

and you now have a new root password.