This covers the data definition language commands in SQL which are used to create structure of Database

1. Data Definition Language
commands in SQL
Mrs. Pallavi Patil

2. Introduction to structural query language
• SQL (Structured Query Language) is used to perform operations on the
records stored in the database such as updating records, deleting records,
creating and modifying tables, views, etc.
• SQL is just a query language; it is not a database. To perform SQL queries,
you need to install any database, for example, Oracle, MySQL, PostGre
SQL, SQL Server, DB2, etc.
Mrs. Pallavi Patil

3. Advantages of SQL
• High speed
• Portable
• Easy to learn and understand
• Supports object oriented programming
• Used with all DBMS system with any vendor
• No coding required
• Used for relational database
• Complete language for database
• Can be used as programming and interactive language
• Dynamic database language
• Client / server language
• Multiple data views
Mrs. Pallavi Patil

4. Data types
• Char
It is used to specify a fixed length string that can contain numbers, letters, and
special characters. Its size can be 0 to 255 characters. Default is 1.
Stud_name char(20)
• Varchar and varchar2:
It is used to specify a variable length string that can contain numbers, letters,
and special characters.
Varchar is used to store maximum data up to 4000 characters
Varchar2 holds variable length character string. Maximum data stored in this
type is 32767 characters.
Stud_name varchar(20)
Mrs. Pallavi Patil

5. • Number (p,s)
It contains precision p and scale s. The precision p can range from 1 to 38, and the
scale s can range from -84 to 127.
Ex. Marks number(5)
• Date
It is used to store a valid date-time format with a fixed length. By default format
for date is DD-MON-YY
birthDate date
Ex. 11-MAR-14
• Long
This datatype is used to store variable length string containing data up to 2 GB.
Mrs. Pallavi Patil

6. Components of SQL
• DDL
 use to create structure of table/ schema.
• DML
 use to manipulate data stored in database.
DQL
 use to fetch the data from database on the basis of perticular condition applied
by user.
• DCL
 DCL commands are used to grant and take back authority from any database
user.
• Transaction Control Language (TCL)
 Use to control different operations performed on records.
Mrs. Pallavi Patil

7. DDL commands
1) CREATE
It is used to create table structure with particular name.
Syntax:
Create table <table_name> (colunmName1 datatype (size), colunmName2
datatype (size),………., colunmNamen datatype (size));
Ex. Create table Student_info(Rollno number(5), Stud_name varchar2(20),
marks number(4,2));
Mrs. Pallavi Patil

8. 2) DESC
This command is used to describe the structure of created table.
Syntax:
DESC table_name;
DESC student_info;
3) ALTER
• This command is used to make changes or modification in the created table.
• With this command we can add , modify or delete columns in the created table.
Syntax 1: For adding new column into table
Alter table < table_name> add ( columnName datatype (size));
Ex. Alter table student_info add (city varchar(10));
Mrs. Pallavi Patil

9. Syntax 2: for modifying created column in table
Alter table < table_name> modify ( columnName datatype (size));
Ex. Alter table student_info modify (city varchar(20));
• Syntax 3: renaming column name
• Alter table <table_name> Rename column <old column_name> to <new
column_name>;
• Syntax 4: For deleting column from existing table
Alter table <table_name> drop (column_name);
Ex. Alter table student_info drop(city);
Mrs. Pallavi Patil

10. 4) RENAME
It is used to change the name of created table.
Syntax:
Rename <old_tablename> to <new_tablename>;
Ex. Rename student_info to student;
5) TRUNCATE
This command is used to remove all records or data from table but table
structure remains as it is database.
Syntax:
Truncate table <table_name>;
Ex. Truncate table student;
Mrs. Pallavi Patil

11. 6) DROP
This command is used to delete or remove entire table structure from
database.
Syntax:
Drop table <table_name>;
Ex. Drop table student;
Mrs. Pallavi Patil