In our programs we use variables to store information. But when our program terminates all the variables declared in it disappear. Why this happens????
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……..
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 ?
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
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………….
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
And they are called DataBase Management System(DBMS). • Oracle • IBM DB2 • Microsoft SQL Server • Microsoft Access • PostgreSQL • MySQL • SQLite
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.
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;
SHOW DATABASES; You will see something like this-
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;
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.
CREATE TABLE [IF NOT EXISTS] table_name( column_list ) type=table_type Example: Suppose I want to create table named “User_Password”
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;
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
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
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
SELECT column_name1,column_name2... FROM tables [WHERE conditions] [GROUP BY group [HAVING group_conditions]] [ORDER BY sort_columns] [LIMIT limits]; Looking very complex
Mostsimple select statement SELECT * FROM table_name; • It selects the whole table; SELECT COLUMN_NAME FROM TABLE • Example: SELECT USERNAME,TYPE FROM USER_PASSWORD;
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‟;
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
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.
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‟;
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‟;
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.