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Introduction to database


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Corrected Introduction to database slide

Corrected Introduction to database slide

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  • 1.  In our programs we use variables to store information. But when our program terminates all the variables declared in it disappear. Why this happens????
  • 2.  What if we need some information to be stored even after the termination of program. (We are here in this session for this need). How can we fulfill this need? Any suggestion……..
  • 3.  The most simple solution is store the information in the disk. Now the question is how we can store in disk. Create a file and store there.(simple enough) Is it a good solution or the best solution ?
  • 4.  Suppose we want to implement the log in section.(feature 1) We use a file and store the user_id and password in the following manner
  • 5.  When 1105120 wants to log in we have to check all the previous record. Also we have to check whether multiple users are accessing the file. Any more problem………….
  • 6.  So we need to care about a lot of facts beside storing, updating the file. But we are lazy people. We always want to minimize our task.(At least me!) Thank GOD there are some applications or Systems which handle the facts about which we were worried 
  • 7.  And they are called DataBase Management System(DBMS). • Oracle • IBM DB2 • Microsoft SQL Server • Microsoft Access • PostgreSQL • MySQL • SQLite
  • 8.  But not all our problems have been solved.  Why??? Because now we have to learn how to maintain Database using DBMS . Here we will see how to manage database using MySQL.
  • 9.  CREATE DATABASE [IF NOT EXISTS] database_name; Example: Suppose I want to create a database named “Quiz”. So the query will be CREATE DATABASE IF NOT EXISTS QUIZ;
  • 10.  SHOW DATABASES; You will see something like this-
  • 11.  DROP DATABASE [IF EXISTS] database_name; Example : Suppose I want to delete the quiz database : So the query will be DROP DATABASE IF EXISTS Quiz;
  • 12.  We have created Database in MySQL. Now we will store data in Database. We store data in Tabular format in MySQL. That means we have to create tables to store data.
  • 13.  CREATE TABLE [IF NOT EXISTS] table_name( column_list ) type=table_type Example: Suppose I want to create table named “User_Password”
  • 14. Query will be: CREATE TABLE USER_PASSWORD( username varchar(6), password varchar(6) ); Username(varchar(6)) Password(varchar(6))
  • 15.  To see the created table in the database use query SHOW TABLES; To see the description of a particular table use query DESCRIBE table_name;
  • 16.  INSERT INTO tbl_name () VALUES(); Example: • INSERT INTO USER_PASSWORD VALUES(„0705001‟,‟123456‟); • INSERT INTO USER_PASSWORD VALUES(„0705002‟,‟678901‟); Username(varchar(6)) Password(varchar(6)) 0705001 123456 0705002 678901
  • 17.  Alter table is used to change the structure of the table Suppose we forgot to add a column in the USER_PASSWORD table. Now we want to add a column name „type‟ in that table
  • 18.  ALTER TABLE USER_PASSWORD ADD COLUMN TYPE VARCHAR(5);Using ALTER TABLE query: • We can also drop column • Rename the table • Change the properties of a column
  • 19.  SELECT column_name1,column_name2... FROM tables [WHERE conditions] [GROUP BY group [HAVING group_conditions]] [ORDER BY sort_columns] [LIMIT limits]; Looking very complex 
  • 20.  Mostsimple select statement SELECT * FROM table_name; • It selects the whole table; SELECT COLUMN_NAME FROM TABLE • Example: SELECT USERNAME,TYPE FROM USER_PASSWORD;
  • 21.  We do not always want to select the whole table .Most of the time part of a table. Example: • SELECT PASSWORD,TYPE FROM USER_PASSWORD WHERE USERNAME = „0705001‟;
  • 22.  Primary key is used to distinguish two rows in a table. Now if I execute INSERT INTO USER_PASSWORD VALUES(„0705001‟,‟hello‟); Username(varchar(6)) Password(varchar(6)) 0705001 123456 0705001 hello 0705002 678901
  • 23.  Big problem. One user two passwords. :O We can avoid it by making USERNAME column as primary key. By making USERNAME column a primary key we ensure that this column will have all distinct value.
  • 24. CREATE TABLE USER_PASSWORD( username varchar(6), password varchar(6), PRIMARY KEY (USERNAME) );
  • 25.  Used to change data in the table. UPDATE table_name SET column_name = value WHERE (Some condition is true); Suppose 0705001 wants to change his/her password. The query will be : UPDATE USER_PASSWORD SET PASSWORD = „1234‟ WHERE USERNAME = „0705001‟;
  • 26.  Usedto delete data in the table. DELETE FROM table_name WHERE (Some condition is true); Suppose we want to throw out an user(0*0*200) from our Database !!! DELTE FROM USER_PASSWORD WHERE USERNAME = „0*0*200‟;
  • 27.  These were very basic database queries. Don‟t be worried if you did not understand all the topics. You will learn all this and many other features in 3-1.
  • 28. THANK YOU