2. What is a database?
a collection of data
Usually consists of entities and
relations
An entity is an individual “object” that exists and is
distinguishable from other individuals.
Example: specific person, company, event, plant
Entities have attributes
Example: people have names and addresses
A relationship is an association among several entities
3. Database Management System
(DBMS)
A computerized record-keeping system
Allows operations such as:
Adding new files
Inserting data into existing files
Retrieving data from existing files
Changing data
Deleting data
Removing existing files from the database
4. Data Models
A data model is a collection of concepts for
describing data.
A schema is a description of a particular
collection of data, using the given data
model.
The relational model of data is the most
widely used model today.
Main concept: relation, basically a table with
rows and columns.
Every relation has a schema, which describes
the columns, or fields.
8. Relational Database Query
A relational database query is a question
about the data, and the answer consists of a
new relation containing the result.
Queries are one part of the Data
Manipulation Language of a DBMS (we also
need to create, update, insert data)
Language: Structured Query Language (SQL)
9. Example SQL query
Select G.Accession, G.Medline
From Genebank G
Where G.source=`baker’s yeast’;
10. No explicit links between
tables
Of course, there may be implicit links
in that two tables share the same
attribute (like the accession number)
In fact, in a relational DB, this is the
only way to connect distinct tables, at
the logical level anyway
A link between one table and another
is called a foreign key
11.
12. Why use a DBMS
Data independence and efficient
access.
Reduced application development
time.
Data integrity and security.
Uniform data administration.
Concurrent access, recovery from
crashes.
13. Example
Suppose you created a file to hold names, ID
numbers and faculty/student status
This was a flat file that resembled a table in
a database
What if you wanted to now add new data for
some of the faculty with credit card
information?
How would you connect the two tables?
15. How to use MySQL
Connect to MySQL Server
shell> ~clement/mysqlbin/bin/mysql -h pathogen.cs.byu.edu –u
cs360 <Enter>
Welcome to the MySQL monitor.
Type 'help' for help.
mysql>
16. How to use MySQL
Data Definition 1
mysql> SHOW DATABASES;
Database
mysql
test
tmp
17. Creating Tables
CREATE TABLE image (
image_id INT,
image_type CHAR(3),
filename CHAR(40),
url CHAR(128),
Primary Key(image_id));
creates a table with 4 columns and no
rows
19. Basic Data Types
INT - signed integer value. Implementation-dependent
# bits
NUMERIC(total length, number of decimal places)
NUMERIC(8,4) - 3 digits, a decimal point, 4 decimal places
REAL - floating point number
BIT - single boolean value
DATE - year, month, day
TIME
TIMESTAMP - date/time
VARCHAR(length) - variable length string <= length
BLOB - Binary Large Object
20. How to use MySQL
INSERT INTO image
( image_id, image_type, filename, url)
VALUES
( 1, ‘jpg’, ‘image1’, ‘http://host/dir/image1’)
Values must be in the right order and fill all columns
Values must be the order specified.
But, you don’t need to fill all columns.
22. Selecting Rows
SELECT image_type from image
WHERE filename=‘image1’
SELECT image_decoder.decoder_program FROM
image_decoder, image
WHERE image.filename=‘image1’
AND
image.image_type=image_decoder.image_type
The Join operation can be viewed as creating a virtual table
on the fly from rows in two or more tables
SELECT * from image GROUP by image_type
23. Basic Where Clauses
Operators
=, <, >, <=, >=, != (or <>)
WHERE image_id = 2
LIKE - wildcard comparison
WHERE decoder_program LIKE ‘c:%’
ISNULL - checks for null value
IN - contained in a set (usually for subqueries)
WHERE image_id IN (1,2)
WHERE image_id IN
SELECT image_id FROM Image
24. Updating Rows
UPDATE Image
SET url=‘http://newhost/image1’
WHERE filename=‘image1’
The where clause may select multiple rows
e.g. WHERE image_id < 50
If the WHERE clause is excluded, the SET
operation is applied to every row in the
table
25. Deleting Rows
DELETE from Image
WHERE image_id=2
Entire row is removed from the table
DELETE from Image
Every row is removed from the table!!!
26. How to use MySQL
Data manipulation 2
mysql> SELECT * FROM seqs;
+-------+-----------+----------+
| title | accession | sequence |
+-------+-----------+----------+
| Human | u235 | cgatcagt |
+-------+-----------+----------+
mysql> insert into seqs
-> values('Dog','u222','ccgtacgt');
mysql> SELECT * FROM seqs;
+-------+-----------+----------+
| title | accession | sequence |
+-------+-----------+----------+
| Human | u235 | cgatcagt |
| Dog | u222 | ccgtacgt |
+-------+-----------+----------+
27. Add data from file
mysql> load data local infile
’/users/faculty/snell/CS360/sample.txt' into
table seqs;
Delete it
mysql> delete from seqs
Redo load with up arrow
select title, accession from seqs;
update seqs set accession = 'H0794' where
title = 'Human-01';
select * from seqs order by title;
31. What Is the Perl DBI?
The standard Database Interface for
Perl
“A perl module and specification that
defines a consistent database interface
independent of the actual database being
used”
32. Why the Perl DBI?
Once upon a time…
One language, many database interfaces
Perl 5 - A new way
Modules and Objects. The DBI is born.
The future is now…
ODBC, Oracle, Informix, Ingres, mSQL, mysql, DB2, Solid,
Sybase, Postgress, Quickbase, Empress, Fulcrum, ...
The same database interface
33. Making simple things easy
and difficult things possible
Goals
Be simple to use for simple applications
Have sufficient flexibility to accommodate unusual
functionality and non-SQL databases
Conform to applicable standards (ODBC etc.)
Enable the creation of database-independent Perl scripts
without being limited to the lowest functionality
Be free.
A ‘higher-level’ interface than ODBC/JDBC
34. Under the Hood
DBI defines and implements an interface
Driver modules do much of the real work
DBI provides default methods, functions, tools etc for
drivers
Not limited to the lowest common denominator -
mechanism provided for driver specific extensions
Designed and built for speed
Valuable detailed call tracing/debugging built-in
35.
36. So why use the Perl DBI?
Because...
It delivers what it promises
It’s here, there and everywhere
It’s fast, flexible and well proven
It’s free, with source
Commercial support is available
It has a large user base and a strong
future
