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Introduction to SQL
Topics covered

Structured Query Language

What can it do?

Advantages of SQL

Why bother with SQL?

The restaurant model

Example SQL usage in PHP
Nic Shulver, [email protected]
Introduction to SQL
What can it do?
SQL provides commands for a variety of tasks
including:
querying data,
inserting, updating, and deleting rows in a table,
creating, replacing, altering, and dropping objects,
controlling access to the database and its objects,
guaranteeing database consistency and integrity.
Nic Shulver, [email protected]
Introduction to SQL
Advantages of SQL
All major relational database management systems
support SQL
You can transfer all skills you have gained with SQL
from one database to another
SQL lets you work with data at the logical level, only
being concerned with the implementation details
when you want to manipulate them. i.e. you do
not need to know how or where data is stored
Nic Shulver, [email protected]
Introduction to SQL
Why bother with SQL?
SQL gives us the power to access the contents
of a database in a simple, powerful way
SQL is (mostly) independent of the underlying
database engine
So you can use SQL with many different kinds
of database
This is simpler than learning how to access
each type of database in a proprietary way
Nic Shulver, [email protected]
Introduction to SQL
The restaurant model
The query engine provides a layer between programming languages and
database.
It allows a developer to write programs which access data, without knowing
how the database is implemented.
Nic Shulver, [email protected]
Introduction to SQL
Example SQL usage in PHP
// grabs matching record(s) from the “tblstudent" table
$sSQL="SELECT * FROM tblstudent WHERE Email='$sEmail' ";
$rsMain = $mysqli->query($sSQL);
What does the SQL do?
How does PHP use SQL?
How does the SQL get sent to the database?
Where do the results of the query appear?
Nic Shulver, [email protected]
Introduction to SQL
SQL to English conversion
$sSQL = "SELECT * FROM student WHERE Email='$sEmail' ";
Select each record from the table called
“tblstudent” where the value of the “Email”
field in the record being checked is equal to
the value held in the PHP variable “$sEmail”.
i.e. grab all the stuff where there’s a match!
$sSQL = "SELECT * FROM student WHERE Email='ab123456' ";
Nic Shulver, [email protected]
Introduction to SQL
Useful SQL SELECT examples
SELECT lastname, age FROM tblstudent WHERE
firstname=‘Naomi’;
SELECT * FROM tblstudent WHERE firstname LIKE ‘Naom*’;
SELECT * FROM tblstudent WHERE age BETWEEN 16 AND
25;
SELECT firstname, studentnumber FROM tblstudent WHERE
age>=25;
SELECT * FROM tblstudent WHERE studentnumber IS NOT
NULL;
Nic Shulver, [email protected]
Introduction to SQL
More SQL SELECT examples
SELECT * FROM tblstudent ORDER BY age DESC;
SELECT * FROM tblstudent WHERE postcode IN(‘ST1’, ‘ST4’,
‘ST6’);
SELECT * FROM tblstudent WHERE age BETWEEN 16 AND 25
ORDER BY age, studentnumber DESC;
SELECT firstname, studentnumber FROM tblstudent WHERE
age>=55 AND studentnumber IS NOT NULL;
SELECT COUNT(*) AS “Total” FROM tblstudent WHERE age>=55;
Nic Shulver, [email protected]
Introduction to SQL
The Four SQL Statements
There are four main SQL statements you will use.
The most useful is SELECT, which we have just seen.
It is usually used in this format;
SELECT column_name(s) FROM table_name
SELECT column_name(s) FROM table WHERE column
operator value
e.g. SELECT lastname, age FROM emp WHERE
firstname=‘Naomi’;
Nic Shulver, [email protected]
Introduction to SQL
The Insert Statement
INSERT INTO table_name VALUES (value1, value2,....)
Inserts a new row into an existing table
INSERT INTO Persons VALUES (‘Lightman', ‘David‘,
‘[email protected]’);
INSERT INTO Authorisation VALUES (‘Joshua’, ‘BURGR’);
Insert Data in Specified Columns
INSERT INTO Persons (LastName, Address) VALUES (‘Smith', '7
Lee Avenue');
Nic Shulver, [email protected]
Introduction to SQL
The Update Statement
UPDATE table_name SET column_name=new_value WHERE
column_name=some_value;
Update one Column in a Row:
UPDATE Person SET FirstName='Bob' WHERE Email='ab123456';
Update several Columns in a Row:
UPDATE Person SET Address='21 Jump Street', City='Los
Angeles' WHERE LastName='Hanson';
Nic Shulver, [email protected]
Introduction to SQL
The Delete Statement
DELETE FROM table_name WHERE column_name =
some_value
Delete one Row:
DELETE FROM Person WHERE Email='ab123456';
Delete several Rows:
DELETE FROM Person WHERE LastName='Smith';
Delete all Rows in a Table: [Beware!]
DELETE FROM Person;
→ Same as: DELETE FROM Person WHERE LastName='*';
Nic Shulver, [email protected]
Introduction to SQL
The Database Connection
 Creates a new connection, configured for student ID codes
// Note: username is “xy123456”, password is “xy123456”
// This is unusual – normally the user, pwd and dbname differ
$id= 'xy123456';
$mysqli = new mysqli("web.fcet.staffs.ac.uk", $id, $id, $id);
if ($mysqli->connect_errno)
{
die( "Failed to connect to MySQL: (" .
$mysqli->connect_errno . ") " . $mysqli->connect_error );
}
Nic Shulver, [email protected]
Introduction to SQL
Using the Statements - Select
// Receives values from Form, assigns values entered to vars
$npage_code = $_REQUEST['code'];
$sSQL = "SELECT * FROM PageElements WHERE
PageCode='$npage_code' ";
$rsSearch = $mysqli->query($sSQL);
// fetches a row of fields and steps to the next one
$row = $rsSearch->fetch_assoc();
// gets each field by name
$linkcode=$row['LinkAd'];
$buycode=$row['BuyAd'];
Nic Shulver, [email protected]
Introduction to SQL
Using the Statements - Insert
// Receives values from Form, assigns values entered to vars
$formname = $_REQUEST["name"];
$formemail = $_REQUEST["email"];
$formcomments = $_REQUEST["comments"];
// Declares SQL statement that will add data to the database
$sSQL = "INSERT INTO users (usrName, usrEmail, usrComments)
VALUES ('$formname', '$formemail', '$formcomments')";
// Just runs the SQL query (but better if we checked for errors)
$mysqli->query($sSQL);
$mysqli->close();
Nic Shulver, [email protected]
Introduction to SQL
Using the Statements - Update
// Declares SQL statement that will update a database
$sSQL = "UPDATE Members SET FirstName='Mike'
WHERE LastName='North' ";
// Executes the SQL…
$mysqli->query($sSQL);
// note that SELECT, UPDATE, DELETE and INSERT
SQL statements all work with the “query()” method
Nic Shulver, [email protected]
Introduction to SQL
Using the Statements - Delete
// Declares SQL statement to delete from a DB
$sSQL="DELETE FROM Members WHERE
CITY='BELFAST' ";
// Executes the SQL statement
If( !$mysqli->query($sSQL) )
{ die("Could not insert into table: " . $mysqli->error);
}
Nic Shulver, [email protected]
Introduction to SQL
Prepared Statements
• Prepared statements use a template system
to avoid SQL injection attacks.
• Example code below – look for the
placeholder character
$stmt = $mysqli->prepare("SELECT id FROM
tblMsgHubUser WHERE tuName=?");
$stmt->bind_param("s", $sUser); // s=string
$stmt->execute();
Nic Shulver, [email protected]
Introduction to SQL
Conclusion
We have seen
What SQL can be used for,
The value of SQL as a cross-platform database
interface language,
Many examples of SQL clauses,
Examples of SQL in PHP.
http://uk3.php.net/manual/en/class.mysqli.php
Nic Shulver, [email protected]