Use and usage of Oracle lead and LGA Functions

Lead:Returns the value of hire_date in the next record.
Select last_name, hire_date,
Lead (hire_date, 1) over (order by hire_date) as "nexthired"
From employees
Where department_id = 30;

Last_name
Hire_dateNexthired
-------------------------------------------
Raphaely
07-dec-9418-may-95

Khoo
18-may-95
24-jul-97
Tobias
24-jul-97
24-dec-97
Baida 
24-dec-97
15-nov-98
Himuro
15-nov-98
10-aug-99
Colmenares
10-aug-99

Lag:Returns the value of hire_date in the previous record (if not, the value is 0 ).
Select last_name, hire_date, salary,
Lag (salary, 1, 0) over (order by hire_date) as prev_sal
From employees
Where job_id = 'pu _ cler ';


Last_name
Hire_date
SalaryPrev_sal
------------------------------------------------------

Khoo
18-may-95