TEC 319Introduction to databases and SQL

What is a database?

A database is an organized way of holding together pieces of information

A database refers to a collection of data and not the means by which it is stored

Software that is used to manage data in a database is known as a database-management system (DBMS)

In a relational database-management system (RDMS), data is stored as a number of different tables that are related to each other in some way

Flat file vs RDBMS

Data can also be stored in a huge flat table

Each row in a flat table contains all the information about a system for that record

The difference between a relational database over a flat table system is that large databases can be constructed from different tables which contain only info relevant to that table

Why choose MySQL?

MySQL is distributed as open source software under the GNU General Public License

It is free to use There are commercial versions where you can purchase

support Even with commercial support, total cost of ownership is

much less than competitors (Oracle, SQL Server) MySQL is robust, powerful and scalable MySQL has replication and clustering to guarantee 100%

availability Extensive user base and wide community support and

adoption (Facebook, Google, Yahoo, Apple, Microsoft, even Oracle)

Majority of website databases run on MySQL It is a desired skill by employers

What is SQL?

Structured Query Language (SQL) It is a common way to retrieve and manage database

information SQL uses descriptive English keywords so most queries

are easy to understand MySQL implementation of SQL conforms to the ANSI SQL

standards We will be learning the basics of SQL and enough to

build simple web applications Extensive database design, transactions, stored

procedures, triggers etc is beyond the scope of this course

Entire courses and major parts of degrees are devoted to database topics

Connecting to MySQL

Using the command lineOpen Applications ->Terminal Emulator in LinuxType:mysql –uroot –p [Press Enter]Enter password: tec319 [Press Enter]

Connecting to MySQL

mysql –uusername –ppasswordORmysql --user=yourname --password

Examplemysql –user=root --passwordEnter password:tec319[Press Enter]

Executing commands

Executing commands

To use a specific databasemysql> \u databasename

mysql> select * from user;

Records are grouped togethermysql> select * from usermysql> \G

Executing commands

Running a script mysql> mysql –user=yourname --

password dbname < script.sql

The above command will execute the sql code in the script.sql tag on the database called dbname.

GUI MySQL Editor

Go to http://localhost/phpMyAdmin in a browser

For user and password enter:root tec319

Basic SQL Syntax

The SELECT statement

Selecting specific columns Syntax Select columnName from Tablename;

egSelect firstName from students;

Selecting multiple columnsSelect firstName, lastName from students;

Selecting all records

In order to retrieve all column values from a table, the * character is used Select * from students;

Remember that the semicolon (;) is needed to terminate a sql query Select * from courses;

Filtering and Sorting Data

Where Clause

Where is added to select statements to tell MySQL to filter the query results based on a given rule

Rules in a WHERE clause refer to data values returned by the query

Only rows that have values which meet the criteria in the rule are returned

Exact match

Syntax exampleSelect firstName, lastName from studentswhere lastName = ‘Smith’;

Select firstName, lastName from studentswhere lastName != ‘Smith’;

Select product_name, product_description from productswhere product_id=3443;

Filtering on a range of values Syntax exampleSelect * from products where price <=9.99;

Select last_namefrom customer_contactswhere last_name > ‘G’;

String values should be surrounded in single quotes

Ordering results – Order By Clause Sorting on a single columnSelect * from productsorder by price;

Select first_name, last_namefrom customer_contactswhere customer_code =‘DEFC’order by last_name;

Sorting on multiple columnsSelect order_date, customer_codefrom ordersorder by order_date, customer_code;

Specifying sort order

The default sort order is ascending depending on the data type of column

e.g Select * from products order by weight; is equivalent toSelect * from products order by weight asc;

If you would like to sort the weight in descending order you can use:Select * from products order by weight desc;

Retrieving Database information Retrieve a list of Databases

Show databases; Retrieve a list of tables

Show tables; Show tables from company;

Here company is the database name

Retrieving a List of Columns Show columns from products;