Web COMP519: Programming Autumn 2008
In the next lectures you will learn What is SQL How to access mySQL database How to create a basic mySQL database How to use some basic queries How to use PHP and mySQL
Introduction to SQL
SQL is an ANSI (American National Standards Institute) standard computer language for accessing and manipulating databases. SQL stands for Structured Query Language using SQL can you can access a database execute queries, and retrieve data insert, delete and update records SQL works with database programs like MS Access, DB2, Informix, MS SQL Server, Oracle, Sybase, mySQL, etc.
Unfortunately, there are many different versions. But, they must support the same major keywords in a similar manner such as SELECT, UPDATE, DELETE, INSERT, WHERE, etc. Most of the SQL database programs also have their own proprietary extensions! The University of Liverpool CS department has a version of mySQL installed on the servers, and it is this system that we use in this course. Most all of the commands discussed here should work with little (or no) change to them on other database systems.
SQL Database Tables
A database most often contains one or more tables. Each table is identified by a name (e.g. "Customers" or "Orders"). Tables contain records (rows) with data.
For example, a table called "Persons":
LastName Hansen Svendson Pettersen
FirstName Ola Tove Kari
Address Timoteivn 10 Borgvn 23 Storgt 20
City Sandnes Sandnes Stavanger
The table above contains three records (one for each person) and four columns (LastName, FirstName, Address, and City).
SQL Queries
With SQL, you can query a database and have a result set returned. A query like this:
SELECT LastName FROM Persons;
gives a result set like this:
LastName Hansen Svendson Pettersen
The mySQL database system requires a semicolon at the end of the SQL statement!
SQL Data Languages
The query and update commands together form the Data Manipulation Language (DML) part of SQL: SELECT - extracts data from a database table UPDATE - updates data in a database table DELETE - deletes data from a database table INSERT INTO - inserts new data into a database table The Data Definition Language (DDL) part of SQL permits database tables to be created or deleted: CREATE TABLE - creates a new database table ALTER TABLE - alters (changes) a database table DROP TABLE - deletes a database table CREATE INDEX - creates an index (search key) DROP INDEX - deletes an index *Here we will use some of them in mySQL
Logging into mySQL Server
You can log into our mySQL server from Linux by typing in the prompt
bash-2.05b$ mysql -h mysql martin u martin
Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 209201 to server version: 5.0.22 Type 'help;' or '\h' for help. Type '\c' to clear the buffer. mysql>
From here you can create, modify, and and drop tables, and modify the data in your tables. But first, you must specify which database on the server you want to use.
mysql> use martin;
Database changed
Technical note
You probably dont need to worry about this, but thought I would mention it here Most books and on-line tutorials assume the database server is running on the same machine as everything else, and that the user is "root". Neither of these are true here. Wherever you see "localhost", replace it by "mysql" Wherever you see "root", replace it with your username.
(Ignore this if you dont understand it for now, or are not consulting other references.)
Creating a Table
You can create a table you might use for the upcoming project. For example,
mysql> CREATE TABLE students( -> num INT NOT NULL AUTO_INCREMENT, -> f_name VARCHAR(48), -> l_name VARCHAR(48), -> student_id INT, -> email VARCHAR(48), -> PRIMARY KEY(num));
Hit Enter after each line (if you want). MySQL doesnt try to interpret the command itself until it sees a semicolon (;) (The -> characters you see are not typed by you.)
Query OK, 0 rows affected (0.02 sec)
*If the server gives you a big ERROR, just try again from the top!
Viewing The Table Structure
Use DESCRIBE to see the structure of a table
mysql> DESCRIBE students;
+------------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+----------------+ | num | int(11) | NO | PRI | NULL | auto_increment | | f_name | varchar(48) | YES | | NULL | | | l_name | varchar(48) | YES | | NULL | | | student_id | int(11) | YES | | NULL | | | email | varchar(48) | YES | | NULL | | +------------+-------------+------+-----+---------+----------------+
Inserting Data
Using INSERT INTO you can insert a new row into your table. For example,
mysql> INSERT INTO students -> VALUES(NULL,Russell,Martin,396310,[e-mail]');
Query OK, 1 row affected (0.00 sec)
Using SELECT FROM you select some data from a table.
mysql> SELECT * FROM students;
+-----+---------+--------+------------+----------------------+ | num | f_name | l_name | student_id | email | +-----+---------+--------+------------+----------------------+ | 1 | Russell | Martin | 396310 | [e-mail] | +-----+---------+--------+------------+----------------------+ 1 row in set (0.00 sec)
Inserting Some More Data
You can repeat inserting until all data is entered into the table.
mysql> INSERT INTO students -> VALUES(NULL,James',Bond',007,'[e-mail]'); Query OK, 1 row affected (0.01 sec)
mysql> SELECT * FROM students; +-----+---------+--------+------------+----------------------+ | num | f_name | l_name | student_id | email | +-----+---------+--------+------------+----------------------+ | 1 | Russell | Martin | 396310 | [e-mail] | | 2 | James | Bond | 7 | [e-mail] | +-----+---------+--------+------------+----------------------+ 2 rows in set (0.00 sec)
Note: The value NULL in the num field is automatically replaced by the SQL interpreter as the auto_increment option was selected when the table was defined.
Getting Data Out of the Table
The SELECT command is the main way of getting data out of a table, or set of tables.
SELECT * FROM students;
Here the asterisk means to select (i.e. return the information in) all columns. You can specify one or more columns of data that you want, such as
SELECT f_name,l_name FROM students;
+---------+--------+ | f_name | l_name | +---------+--------+ | Russell | Martin | | James | Bond | +---------+--------+ 2 rows in set (0.00 sec)
Getting Data Out of the Table (cont.)
You can specify other information that you want in the query using the WHERE clause. SELECT * FROM students WHERE l_name=Bond;
+-----+---------+--------+------------+----------------------+ | num | f_name | l_name | student_id | email | +-----+---------+--------+------------+----------------------+ | 2 | James | Bond | 7 | [e-mail] | +-----+---------+--------+------------+----------------------+ 1 row in set (0.00 sec)
SELECT student_id, email FROM students WHERE l_name=Bond;
+------------+----------------------+ | student_id | email | +------------+----------------------+ | 7 | [e-mail] | +------------+----------------------+ 1 row in set (0.00 sec)
Altering the Table
The ALTER TABLE statement is used to add or drop columns in an existing table.
mysql> ALTER TABLE students ADD date DATE;
Query OK, 2 rows affected (0.00 sec) Records: 2 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM students; +-----+---------+--------+------------+----------------------+------+ | num | f_name | l_name | student_id | email | date | +-----+---------+--------+------------+----------------------+------+ | 1 | Russell | Martin | 396310 | [e-mail] | NULL | | 2 | James | Bond | 7 | [e-mail] | NULL | +-----+---------+--------+------------+----------------------+------+ 2 rows in set (0.00 sec)
Updating the Table
The UPDATE statement is used to modify data in a table.
mysql> UPDATE students SET date='2007-11-15' WHERE num=1;
Query OK, 1 row affected (0.01 sec) Rows matched: 1 Changed: 1 Warnings: 0
mysql> SELECT * FROM students; +-----+---------+--------+------------+----------------------+------------+ | num | f_name | l_name | student_id | email | date | +-----+---------+--------+------------+----------------------+------------+ | 1 | Russell | Martin | 396310 | [e-mail] | 2007-11-15 | | 2 | James | Bond | 7 | [e-mail] | NULL | +-----+---------+--------+------------+----------------------+------------+ 2 rows in set (0.00 sec)
Note that the default date format is YYYY-MM-DD and I dont believe this default setting can be changed.
Deleting Some Data
The DELETE statement is used to delete rows in a table.
mysql> DELETE FROM students WHERE l_name='Bond';
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM students; +-----+---------+--------+------------+----------------------+------------+ | num | f_name | l_name | student_id | email | date | +-----+---------+--------+------------+----------------------+------------+ | 1 | Russell | Martin | 396310 | [e-mail] | 2006-11-15 | +-----+---------+--------+------------+----------------------+------------+ 1 row in set (0.00 sec)
The Final Table
Well first add another column, update the (only) record, then insert more data.
mysql> ALTER TABLE students ADD gr INT; Query OK, 1 affected row (0.01 sec) Records: 1 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM students; +-----+---------+--------+------------+----------------------+------------+------+ | num | f_name | l_name | student_id | email | date | gr | +-----+---------+--------+------------+----------------------+------------+------+ | 1 | Russell | Martin | 396310 | [e-mail] | 2007-11-15 | NULL | +-----+---------+--------+------------+----------------------+------------+------+ 1 row in set (0.00 sec) mysql> UPDATE students SET gr=3 WHERE num=1; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0
mysql> SELECT * FROM students; +-----+---------+--------+------------+----------------------+------------+------+ | num | f_name | l_name | student_id | email | date | gr | +-----+---------+--------+------------+----------------------+------------+------+ | 1 | Russell | Martin | 396310 | [e-mail] | 2007-11-15 | 3 | +-----+---------+--------+------------+----------------------+------------+------+ 1 row in set (0.00 sec) mysql> INSERT INTO students VALUES(NULL,James',Bond',007,'[e-mail],200711-15, 1); . . . . . .
The Final Table (cont.)
. . . . . . mysql> INSERT INTO students VALUES(NULL,Hugh,Milner',75849789,[e-mail], CURRENT_DATE, 2);
Note: CURRENT_DATE is a built-in SQL command which (as expected) gives the current (local) date.
mysql> SELECT * FROM students; +-----+---------+----------+------------+----------------------------+------------+------+ | num | f_name | l_name | student_id | email | date | gr |
+-----+---------+----------+------------+----------------------------+------------+------+ | | | | | | | 1 | Russell | Martin 5 | Kate 3 | James 4 | Bob 6 | Pete 7 | Polly 8 | Hugh | Ash | Bond | Jones | Lofton | | | | | 396310 | [e-mail] 124309 | [e-mail] 7 | [e-mail] 12190 | [e-mail] | 2007-11-15 | | 2007-11-16 | | 2007-11-15 | | 2007-11-16 | 3 | 3 | 1| 3 | 2 | 1| 2 |
76 | [e-mail] | 2007-11-17 | 1717 | [e-mail] 75849789 | [e-mail] | 2007-11-17 | | 2007-11-17 |
| Crackers | | Milner |
+-----+---------+----------+------------+----------------------------+------------+------+ 7 rows in set (0.00 sec) mysql> exit Bye
Other SQL Commands
SHOW tables; gives a list of tables that have been defined in the database ALTER TABLE students DROP email; would drop the email column from all records DROP TABLE students; deletes the entire students table, and its definition (use the DROP command with extreme care!!) DELETE FROM students; removes all rows from the students table (so once again, use the DELETE command with great caution), the table definition remains to be used again A more useful command is something like DELETE FROM students WHERE (num > 5) AND (num <= 10); which selectively deletes students based on their num values (for example). HELP; gives the SQL help HELP DROP; gives help on the DROP command, etc.
Backing up/restoring a mySQL database
You can back up an entire database with a command such as
mysqldump h mysql u martin martin > backup.sql
(Run from the Unix command line.) This gives a script containing SQL commands to reconstruct the table structure (of all tables) and all of the data in the table(s). To restore the database (from scratch) you can use this type of Unix command:
mysql h mysql u martin martin < backup.sql
Other commands are possible to backup/restore only certain tables or items in tables, etc. if that is what you desire. For example
mysqldump h mysql u martin martin books clients> backup.sql
stores information about the books and clients tables in the martin database.
Putting Content into Your Database with PHP
We can simply use PHP functions and mySQL queries together: Connect to the database server and login (this is the PHP command to do so) mysql_connect("host","username","password"); Choose the database mysql_select_db("database");
Host: Database: Username: Password: mysql martin martin <blank>
Send SQL queries to the server to add, delete, and modify data mysql_query("query"); (use the exact same query string as you would normally use in SQL, without the trailing semi-colon) Close the connection to the database server (to ensure the information is stored properly) mysql_close(); Note: For this to work properly on the UoL server, you must access the PHP script through the cgi server (http://cgi.csc.liv.ac.uk/~martin/getstuff.php for example).
Student Database: data_in.php
<html> <head> <title>Putting Data in the DB</title> </head> <body> <?php /*insert students into DB*/ if(isset($_POST["submit"])) { $db = mysql_connect("mysql, martin"); mysql_select_db("martin"); $date=date("Y-m-d"); /* Get the current date in the right SQL format */
$sql="INSERT INTO students VALUES(NULL,' . $_POST[f_name"] . "',' . $_POST["l_name"] . "', . $_POST["student_id"] . ",' . $_POST["email"] . "',' . $date . "', . $_POST["gr"] . ")"; /* construct the query */ mysql_query($sql); mysql_close(); /* execute the query */
echo"<h3>Thank you. The data has been entered.</h3> \n"; echo'<p><a href="data_in.php">Back to registration</a></p> . \n; echo'<p><a href="data_out.php">View the student lists</a></p> .\n; }
Student Database: data_in.php
else { ?> <h3>Enter your items into the database<...