Ex: NO:1 SQL QUERIES FOR CREATION OF DATABASE
Aim:
To execute the queries to create and alter the schema of the database.
Data Definition in SQL
Creating Tables:
The SQL command for creating an empty table has the following form:
Syntax:
create table <table-name> (<column 1> <data type> ,<column2t> <data type>, . . . , .<column n> <data type>, <integrity constraint1>,…., <integrity constraint n>);
Example:
The create table statement for EMP table has the form
create table EMP (EMPNO number(4), ENAME varchar2(30), JOB varchar2(10), MGR number(4), HIREDATE date, SAL number(7,2), DEPTNO number(2));
Deleting tables:
The following command will drop the table from the database.
Syntax:
drop table <table-name>;
Example:
drop table emp;
Alter table:
Alter table command is used to add, modify or drop attributes or columns from the table.
Syntax:
alter table <table-name> add/modify <col-name1> <datat ype>,….,<col-namen> <data type>;
alter table <table-name> drop <col-nmae>;
Example:
alter table emp add year char(3);
Truncate table:
The truncate table command deletes the rows in the table but retains the table structure.
Syntax:
truncate table <table-name>;
Example:
truncate table emp;
Describe table:
This command is used to view the schema of the table
Syntax:
desc <table-name>;
Result:
The commands to create and alter the schema of the database are executed.