1 A Very Brief Introduction to Relational Databases

2 Database Management Systems DBMS vs. Files Files hold data. Knowledge of the structure is in the programs that use the files. Example: Addresses.csv Files can hold complex data structures Each program must know how the data is represented in the file. Any change to the representation requires changes to all programs that access the file

3 Database Management Systems A DBMS holds both data and structure Decouples programs from the details of how the data is represented. Permits programs to say what they want in more abstract terms. Simple Example: Give me all the records with zip codes beginning with 336 vs Read each record. Extract the first three digits of the zip code. Skip over the record if not 336. Much more complex operations are possible.

4 Database Management Systems Changes to the structure do not necessarily require changes to the programs that access the data. There is a startup cost Once you have learned the basics, using a DBMS is much easier than writing code to process file data directly.

5 Database Management Systems Have long been the mainstay of large scale data processing. Now readily available for personal computers The.NET Framework provides good support Smooth integration with C# and VB Supported by Visual Studio Used by most real world web sites.

6 Relational Database Specific form of DBMS Invented by E.F. Codd of IBM “ A Relational Model of Data for Large Shared Data Bank” Communications of the ACM; 13(6); 1970 First commercial product produced in 1979 by Relational Software, Inc. Today known as Oracle Corp. Extensive theoretical underpinnings Books, Courses, Career Fields

7 Relational Database Data is organized as tables Rows and columns Basic concept: Every distinct of piece of information is held in only one place. Entries in different tables are related when they have the same value for a field used as a key. Operations permit data from related tables to be combined to answer complex questions. Give me the Product_Description from the Products table entry with Product_ID matching the Product_ID in each Order_Item in the Order_Details table having an Order_ID matching the Order_ID in Current_Invoice.

8 Database Management System The DBMS is a server Often on a dedicated computer. Small version may reside on a PC. Always a separate entity Not a part of the operating system Users and user programs interact with the database server to retrieve and update information in the database.

9 SQL Structured Query Language Industry standard langauge for accessing and manipulating relational databases. Prototype developed by Codd at IBM Now an ANSI and ISO standard Latest version SQL-99 aka SQL-3 Every vendor has its own version Core language fairly consistent Have to learn vendor’s extensions

10 SQL SQL can be used both interactively and by programs. Commands called queries. Run a program for interactive use. The.NET Framework supports access by Windows programs. Programs create query strings to say what they want. Different meaning from query strings in HTML. Same as the strings you might type on a command line for an interactive program. Compiler and runtime system have no understanding of the string.

11 LINQ Visual Studio 2008 and later supports a new feature called LINQ. Language Integrated Query Introduced in.NET Framework 3.5 Permits us to write C# and VB statements to do queries rather than just composing strings and sending them to the server. The compiler can check the syntax (unlike query strings.) Permits queries against data structures as well as databases. Entity Framework Automates production of code to access data Visual Studio 2010 and later

12 Tables All data in a relational database is in Tables To create a table: Specify a name for the table Define columns Specify name for the column Specify data type. Similar but not identical to types in programming languages. Caution: This is just a start. There is a lot more to know about creating a database.

Organization of Data Table should not include multiple columns for the same infomation. Example Table Classes might hold information about various classes being taught in the current semester. One row per class Course number, classroom, times, etc. Not students. Multiple students per class. Variable number of students in class. 13

Organization of Data Students would be in a separate table. One row per student. Another table relates students to classes. One row per student-class pair Identifies class Identifies student Says that this student is in this class 14

15 SQL Sessions Users can interact with a database system, using a program running on their local computer. Command line or GUI Generally must log in with the server User name and password This creates a session. May need to specify a particular database, or one may be determined automatically by user name.

16 SQL Sessions Once logged in, you can Create tables Add entries to tables Modify existing data Retieve information from tables Delete entries from table Delete tables providing you have the relevant privilege Programs can do these same things

17 Database Connections Before a user or a program can interact with a Database system, there must be a connection into the database. An interactive session establishes a connection when logging in. A program must connect to a database by passing a connection string string to the server. Specifies user name and desired database May specify password. Possibly lots of other stuff. Very easy to mess up!

18 Types of SQL Commands DDL Data Definition Language Create and restructure tables DML Data Manipulation Language Change data in tables DQL Data Query Langauage Retrieve information from tables Others Database administration Advanced concepts

19 Data Definition Language CREATE TABLE ALTER TABLE DROP TABLE CREATE INDEX ALTER INDEX DROP INDEX CREATE VIEW DROP VIEW SQL commands are free form Not case sensitive

20 Example: CREATE TABLE CommandTable Name Column NameData Type CREATE TABLE INSTRUCTOR (INSTRUCTOR_ID NUMBER(8,0), SALUTATION VARCHAR2(5), FIRST_NAME VARCHAR2(25), LAST_NAME VARCHAR2(25), STREET_ADDRESS VARCHAR2(50), ZIP VARCHAR2(5), PHONE VARCHAR2(15) )

21 Data Manipulation Language INSERT UPDATE DELETE

Insert a new row into table Book INSERT INTO Book (book_id, title, publisher, publish_date) VALUES (1013, 'Jane Eyre', 'Random House', '12/2013') 22 INSERT Example Table Name Column Names Values for new row Column names may be omitted if a value is provided for every column (in the right order.)

INSERT Example Identity Column Server picks a unique value automatically. Cannot be specified by the user. If book_id is an Identity Column: INSERT INTO Book (title, publisher, publish_date) VALUES ('Jane Eyre', 'Random House', '12/2013') Server chooses a unique value for book_id 23

24 Data Query Language SELECT Only one command Many options and clauses Primary method of interacting with the database Interactive users Programs

SELECT title, publisher FROM book WHERE title = ' Jane Eyre ' Example from a C# program: strSQL = "SELECT * FROM Orders " + " WHERE Store_ID = " + Store_ID.ToString() + " AND Order_ID = " + Order_ID.ToString(); 25 Examples: SELECT Column Names Table Name * means “All Columns” “Where” clause specifies which rows to return These are local variables in the C# program. End of Presentation