1. 1 Databases & SQL By: Julia Tartakovsky CS 340, Fall 2004 Acknowledgement (for help with the J# code connecting to an Oracle DB): Yosef Lifshits

2. 2 Database Management System (DBMS) A DBMS is: –A collection of interrelated data (a database), and –A set of programs to access the data DBMS provides an environment that is both convenient and efficient to use. Database Applications: –Banking: all transactions –Airlines: reservations, schedules –Universities: registration, grades –Sales: customers, products, purchases –Manufacturing: production, inventory, orders, supply chain –Human resources: employee records, salaries, tax deductions

3. 3 Purpose of Database System In the early days, database applications were built on top of file systems –We are managing data in this way even today –E.g. using Windows Explorer to find your files Drawbacks of using file systems to store data: –Data redundancy and inconsistency Multiple file formats, duplication of information in different files –Difficulty in accessing data Need to write a new program to carry out each new task –Data isolation — multiple files and formats –Integrity problems Integrity constraints (e.g. account balance > 0) become part of program code Hard to add new constraints or change existing ones

4. 4 Purpose of Database Systems (Cont.) Drawbacks of using file systems (cont.) –Atomicity of updates Failures may leave database in an inconsistent state with partial updates carried out E.g. transfer of funds from one account to another should either complete or not happen at all –Concurrent access by multiple users Concurrent accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies –E.g. two people reading a balance and updating it at the same time –Security problems Database systems offer solutions to all the above problems

5. 5 Application Architectures  Two-tier architecture: E.g. client programs using ODBC/JDBC to communicate with a database  Three-tier architecture: E.g. web-based applications, and applications built using “middleware”

6. 6 Levels of Abstraction Physical level describes how a record (e.g., customer) is stored. Logical level: describes data stored in database, and the relationships among the data. type customer = record name : string; street : string; city : integer; end; View level: application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes.

7. 7 View of Data An architecture for a database system

8. 8 Schemas and Instances Analogous to types and variables in programming languages Schema – the logical structure of the database –e.g., the database consists of information about a set of customers and accounts and the relationship between them –Analogous to type information of a variable in a program –Physical schema: database design at the physical level –Logical schema: database design at the logical level Instance – the actual content of the database at a particular point in time –Analogous to the value of a variable Physical Data Independence – the ability to modify the physical schema without changing the logical schema –Applications depend on the logical schema –In general, the interfaces between various levels and components should be well defined so that changes in some parts do not seriously influence others.

9. 9 Data Models A collection of conceptual tools for describing –data –data relationships –data semantics –data constraints Entity-Relationship model Relational model Other models: –object-oriented model –Object-relational model –semi-structured data models, XML

10. 10 Entity-Relationship Model Example of schema in the entity-relationship model:

11. 11 Entity Relationship Model (Cont.) E-R model of real world –Entities (objects) E.g. customers, accounts –Relationships between entities E.g. Account A-101 is held by customer Johnson Relationship set depositor associates customers with accounts Widely used for database design –Database design in E-R model usually converted to design in the relational model (coming up next) which is used for storage and processing

12. 12 Relational Model A collection of tables Example of tabular data in the relational model customer- name Customer- id customer- street customer- city account- number Johnson Smith Johnson Jones Smith 192-83-7465 019-28-3746 192-83-7465 321-12-3123 019-28-3746 Alma North Alma Main North Palo Alto Rye Palo Alto Harrison Rye A-101 A-215 A-201 A-217 A-201 Attributes

13. 13 A Sample Relational Database

14. 14 What is SQL? SQL (pronounced "ess-que-el") stands for Structured Query Language. SQL is used to communicate with a database. SQL statements are used to perform tasks such as: –update data on a database (an action query) –retrieve data from a database (a select query)

15. 15 What is SQL? (cont.) Relational database management systems that use SQL: –Oracle –Sybase –Microsoft SQL Server –Access –Ingres Standard SQL commands: –"Select“ –"Insert" –"Update“ –"Delete“ –"Create“ –"Drop"

16. 16 SQL SQL: widely used non-procedural language –E.g. find the name of the customer with customer-id 192-83-7465 select customer.customer-name from customer where customer.customer-id = ‘192-83-7465’ –E.g. find the balances of all accounts held by the customer with customer-id 192-83-7465 select account.balance from depositor, account where depositor.customer-id = ‘192-83-7465’ and depositor.account-number = account.account-number

17. 17 SELECT For more examples and an interactive environment, go to: http://sqlcourse.com/select.html

18. 18 SELECT with “distinct” Eliminate identical records.

19. 19 Aggregate with distinct For more examples and an interactive environment, go to: http://sqlcourse2.com/agg_functions.html

20. 20 Group-by Grouping tuples with identical attributes. For more examples and an interactive environment, go to: http://sqlcourse2.com/groupby.html

21. 21 Summarized information by groups

22. 22 Group by with “having” Cutting un-wanted groups after group by For more examples and an interactive environment, go to: http://sqlcourse2.com/having.html

23. 23 Join The result table removes meaningless tuples from the cartesian product.

24. 24 Join with group-by and having QUESTION: What is the meaning of this query?

25. 25 CREATE Table CREATE TABLE table-name (attr1 attr-type PRIMARYKEY, attr2 attr-type,…,attrN attr-type); Adds a new table with the specified attributes (and types) to the database. http://sqlcourse.com/create.html http://sqlcourse.com/create.html For more examples and an interactive environment, go to: http://sqlcourse.com/create.html http://sqlcourse.com/create.html

26. 26 Access Data Types Numeric (1, 2, 4, 8 bytes, fixed or float) Text (255 max) Memo (64000 max) Date/Time (8 bytes) Currency (8 bytes, 15 digits + 4 digits decimal) Autonumber (4 bytes) Yes/No (1 bit) OLE (limited only by disk space) Hyperlinks (up to 64000 chars)

27. 27 Access Numeric types Byte –Stores numbers from 0 to 255 (no fractions). 1 byte Integer – Stores numbers from –32,768 to 32,767 (no fractions) 2 bytes Long Integer(Default) –Stores numbers from –2,147,483,648 to 2,147,483,647 (no fractions). 4 bytes Single –Stores numbers from -3.402823E38 to –1.401298E–45 for negative values and from 1.401298E–45 to 3.402823E38 for positive values.4 bytes Double –Stores numbers from –1.79769313486231E308 to – 4.94065645841247E–324 for negative values and from 1.79769313486231E308 to 4.94065645841247E–324 for positive values.158 bytes Replication ID –Globally unique identifier (GUID)N/A16 bytes

28. 28 Oracle Data Types CHAR (size) -- max 2000 VARCHAR2(size) -- up to 4000 DATE DECIMAL, FLOAT, INTEGER, INTEGER(s), SMALLINT, NUMBER, NUMBER(size,d) –All numbers internally in same format… LONG, LONG RAW, LONG VARCHAR –up to 2 Gb -- only one per table BLOB, CLOB, NCLOB -- up to 4 Gb BFILE -- file pointer to binary OS file

29. 29 Creating a new table from existing tables Syntax: –SELECT [DISTINCT] attr1, attr2,…, attr3 INTO newtablename FROM rel1 r1, rel2 r2,… rel3 r3 WHERE condition1 {AND | OR} condition2 ORDER BY attr1 [DESC], attr3 [DESC]

30. 30 ALTER Table ALTER TABLE table-name ADD COLUMN attr1 attr-type; … DROP COLUMN attr1; … DROP COLUMN attr1; Adds a new column to an existing database table.

31. 31 INSERT INSERT INTO table-name (attr1, attr4, attr5,…, attrK) VALUES (“val1”, val4, val5,…, “valK”); Adds a new row(s) to a table. INSERT INTO table-name (attr1, attr4, attr5,…, attrK) VALUES SELECT... http://sqlcourse.com/insert.html http://sqlcourse.com/insert.html For more examples and an interactive environment, go to: http://sqlcourse.com/insert.html http://sqlcourse.com/insert.html

32. 32 DELETE DELETE FROM table-name WHERE ; Removes rows from a table. http://sqlcourse.com/delete.html http://sqlcourse.com/delete.html For more examples and an interactive environment, go to: http://sqlcourse.com/delete.html http://sqlcourse.com/delete.html

33. 33 UPDATE UPDATE tablename SET attr1=newval, attr2 = newval2 WHERE ; changes values in existing rows in a table (those that match the WHERE clause). http://sqlcourse.com/update.html http://sqlcourse.com/update.html For more examples and an interactive environment, go to: http://sqlcourse.com/update.html http://sqlcourse.com/update.html

34. 34 DROP Table DROP TABLE tablename; Removes a table from the database. For more examples and an interactive environment, go to: http://sqlcourse.com/drop.html

35. 35 J# Source Code Connecting to an Oracle DB

36. 36 Screenshot of J# Program Output

37. 37 Questions? For a neat SQL tutorial and an interactive environment, go to: http://sqlcourse2.com/intro2.html