SQL: DDL(Data-Definition Language)

DDL commands used for design or defines database.

in DDL create,alter,truncate,drop commands include.

CRATE

crate command used to create a table in database.
syntax

   CRATE TABLE <table name>
                   (
                   <column 1> <datatype> (<size>),
   <column 2> <datatype> (<size>),
                   );

Example

CREATE TABLE student
                                 (
                                  id number(6),
            name varchar2(30),
                                  phone number(10)
                                  );

ALTER

Alter command used modify structures of a table.
Alter command used add ,modify, or drop table columns in a table.
syntax

Adding New Columns

   ALTER TABLE <tablename>
               Add (NewColumnName Datatype(size),
                        NewColumnName Datatype(size)….);

               EXAMPLE
   ALTER TABLE student ADD(address varchar2(100));

Modifying Existing Columns

ALTER TABLE TableName
MODIFY (ColumnName NewDatatype(NewSize));

EXAMPLE

ALTER TABLE student MODIFY(id number(10));

Dropping(deleting) Existing Columns

ALTER TABLE <TableName> DROP COLUMN <columname>;

EXAMPLE

ALTER TABLE student DROP COLUMN phone

TRUNCATE TABLE

TRUNCATE TABLE used to delete all data from a table.
this command deletes all rows

syntax

TRUNCATE TABLE <TableName>;

EXAMPLE
TRUNCATE TABLE student;

DROP TABLE

DROP TABLE command is used to delete table from a database.

syntax

DROP TABLE <TableName>;

EXAMPLE

DROP TABLE student;