Topic 1: Introduction to SQL

• SQL stands for Structured Query Language.• SQL is a standard computer language for

accessing and manipulating databases• SQL is the set of commands that is recognized

by nearly all RDBMS.

SQL commands can be divided into following categories.

• Data Definition Language (DDL)• Data Manipulation Language (DML) • Transaction Control Language (TCL)

DDL (Data Definition Language) Commands:

• These commands are used for creation; alteration and removal of database objects e.g.: CREATE TABLE, ALTER TABLE, and DROP TABLE.

DML (Data Manipulation Language) Commands:

• These commands are used to add, modify or remove the data contained in the database tables. e.g.: INSERT, DELETE, UPDATE, SELECT etc. are DML commands.

TCL (Transaction Control Language) Commands

• These commands are used to start or end transactions. e.g.: COMMIT, ROLLBACK, ROLL BACK TO etc. are TCL commands.

Topic 2: DDL commands

• Note: All commands given below are based on the table Student:

• Table: Student CREATE is used to create a table. The syntax of this command is:

• create table tablename(column1name datatype [constraint],column2name datatype [constraint], column3name datatype [constraint]);

• Keywords specifying Items that may be created• table • Data Types• char(size) - Fixed length string of characters of the set size. The size

of the string is limited to 255 characters. • date • number(maxsize) - Number with a maximum number of digits

specified by "maxsize". • number(maxdigits,maxright) - A decimal number with a manimum

number of "maxdigits" with "a maximum number of digits to the right of the decimal, "maxright".

• varchar(maxsize) - A character string with variable lingth limited to "maxsize".

• Constraints• Constraints are rules for the column.. Possible values include: • not null - The column values must have a value and cannot be null. • primary key - Each record is uniquely identified by this column. • unique - No two values may be the same in the column

Example

• create table citylist(name varchar(20),state varchar(20),population number(8),zipcode number(5) unique);

STUDENT

Name Roll Class Age Marks

Raghav 101 C12 15 91

Ajay 102 M12 14 92

Gagan 103 C12 15 80

Shika 104 E12 14 85

Delete table:

• Drop table name• Example drop student;

Topic 3:DML command

• INSERT INTO: A row or tuple can be inserted in an existing table with the help of an INSERT command.It is DML command

• Syntax:• Insert into tablename [column list] values

(val1, val2,…)• Note: Values should be inserted in the same

order as table creation.

• Example: Write a command to insert a row in the table student.

• Ans: Insert into student values (‘ahmed’, 105, C12, 16, 98);

• • UPDATE STATEMENT: Update command is

used to make changes to the existing values.

Example 1: Write a command to change the marks from 40 to 86 for

rollno 2

• Ans: Update Student Set marks =86 where rollno = 2;

Example 2: Write a query to change the marks as 95 and grade a A+ for

rollno 31.

• Ans: Update Student set marks=95 and grade=’A+’ where rollno = 31;

Example 3: Write a command to update all the marks by adding 5

marks for all students.

• Ans: Update Student set marks = marks +5;

Example 4: Write a command to change the grade as A for all students

whose marks is greater than 90.• Ans: Update Student set grade=’A’ where

marks > 90;

• Next class

• DELETE COMMAND: This command is used to delete one row or more than one row.

• Example: Write a command to delete the details of students who have scored less than 33 marks.

• Ans: Delete from Student where marks < 33;

• SELECT: The SELECT statement is used to select data from a table. The tabular result is stored in a result table (called the result-set).

• Syntax: • SELECT [ALL | DISTINCT] columnname1

[,columnname2]FROM tablename1 [,tablename2][WHERE condition] [ and|or condition...][GROUP BY column-list][HAVING "conditions][ORDER BY "column-list" [ASC | DESC] ]

• Note: SQL statements are not case sensitive. SELECT is the same as select.

• Example 1: Select * from student;• Example 2: Select all from student;• The above two commands display all the

details from the table Student.• • Example 3: Select name, marks from student;• This command will display only the name &

marks columns from the table student.• • Example 4: Select Distinct class from student;

• DISTINCT can be used to select column names and values deleting duplicates.

• Output: • Class• C12• M12• E12

• WHERE clause: The WHERE clause is used to specify a selection criterion.

• To conditionally select data from a table, a WHERE clause can be added to the SELECT statement.

Syntax

SELECT column FROM tableWHERE column operator value

With the WHERE clause, the following operators can be used:

Operator Description= Equal<> Not equal> Greater than< Less than>= Greater than or equal

<= Less than or equalBETWEEN Between an inclusive rangeLIKE Search for a patternIN If you know the exact value you

want to return for at least one of the columns

Example 1: Select name, marks from student where age > 14;

Name Marks

Raghav 90

Gagan 90

Example 2: Write a query to display all details about the students whose age

is 15.• Ans: Select * from Student where age=15;

Example 3: Write a query to display name, roll and class of all students

whose marks is above 90.

• Ans: Select name, roll, class from Student where marks > 90;

Example 4: Write a query to display the name and age of students who

belong to class C12.

• Ans: Select name, age from student where class = ‘C12’;