Cross Join:
===========
When we want to retrieve the data or info by joining the rows of two tables we can use "cross join".

Ex: by joining the row-1 of table-1 with row1 of table-2 and 
row-1 of table-1 with row-2 of table-2 ==> cross join

syntax:
-------
	select columns
	from tabl-1
	cross join
	table-2
	order by
	columns;

Scenario:
----------
Generating the weekly menu of the restaurant

Solution:
---------
1) create the table with the name of "dayName" by including:
	dayId
	day
by using the below syntax:

create table dayName
(
	dayId number,
	day varchar(15)
);

2) create another table with the name of "dishes" by including:
	dishId
	dishName
by using the below syntax:

create table dishes
(
	dishId number,
	dishName varchar(30)
);

3) Insert the data into both the tables:
by using the below syntax:

insert into dayName values(&dayId, &day);
insert into dishes values(&dishId, &dishName);

4) Cross join:
---------------
select 
d1.dishName,
d2.day
from 
dishes d1
cross join
dayName d2
order by
d1.dishId, d2.dayId;

===================================================================================
Events:
=======
=> three types of events in SQL:
	1) insert
	2) update
	3) delete

Triggers:
=========
==> Trigger is a stored procedure that automatically executes in response to an event.

How to create the trigger:
--------------------------
Scenario:
Employees with Audit Information

procedure:
----------
1) create the tables:

create table employees
(
eid number primary key,
ename varchar(100) not null,
dept varchar(50)
);

create table emp_audit
(
auditId number primary key,
eid number,
ename varchar(100),
auditDate date
);

2) create a sequence for auditId start with '1' and increment by '1'
--------------------------------------------------------------------
Syntax:
-------
	create sequence sequence-name start with start-value increment/decrement by step;

create sequence emp_audit_seq start with 1 increment by 1;

Note:
----
sequence creation for triggers is optional
because we allowed to create the sequence within the trigger definition.

3) create the trigger:
-----------------------
Syntax:
-------
create or replace trigger trigger-name
event-name
for each row
begin
event definition
end;
/

create or replace trigger trigger_emp_insert_audit
after insert on employees
for each row
begin
insert into emp_audit values(emp_audit_seq.NEXTVAL,
	:NEW.eid,
	:NEW.eName,
	sysdate);
end;
/