select sysdate  //your system date 
from dual 

10-Apr-2020

//Add Months fucntion 
select add_months( sysdate , 3 ) //The number of months that you want to add 
from dual 
10-Jul-2020

select add_months(hire_date, 5)  //17-nov-1985
from employees   //17-apr-1986


select round((sysdate - hire_date)/12) "The number of months"
from employees

//Months between function 
select round(months_between( sysdate , hire_date )) "The number of months"
from employees  

//Next day function 
Next_day( sysdate , ' friday ' )
from dual
17-apr-2020
it will give you the date of the next day represented in the second parameter 
Next_day( sysdate  , 'Tuesday' ) 
next_day(hire_date , 'Sunday')
select next_day(sysdate,'Tuesday')
from dual 

14-Apr-2020

//Last day function 
will give you the date of the last day in the month

employee = 13-sep-1990 => hire_date => 31-sep-1990
select last_day(hire_date)
from employees

select last_day(sysdate)
from dual

30-Apr-2020

//Extract function 
you can extract a specific information from the date and 
display it on screen 
 
select extract(day from sysdate)
from dual //10
select extract(month from sysdate)
from dual //4
select extract(year from sysdate) 
from dual //2020

// Round and Trunc Functions 
number .5 => to next number => 7.5 => 8 => round
number .5 => to next number => 7.5 => 7.5 => Trunc
number .3 => to next number => 7.3 => 7 => round
number .3 => to next number => 7.3 => 7 => Trunc

02:55 pm
select round(sysdate)
from dual   
10-Apr-2020 12:00 am     0-9  
round(sysdate, "year")   12 => 6   .. 7 > 6
17-jul-2020 => 01-jan-2021
10-apr-2010
1-jan-2010

round(sysdate, "month")  30 => 15  .. 15 >= 
15-jul-2010
01-Aug-2010
10-jul-2010
1-jul-2010
round(sysdate, "day")     24 == 12 pm 
14-jun-2020  10:00 am => 14-jun-2020 12:00 am
17-jul-2010  2:30 pm
18-jul-2010

//Formats for the year
YYYY,YYY,YY,Y: Four-digit year. Last 3,2,1 digits in the year
2020,020,20,0 
Year = two thousand and twenty 

//Formats for the months
MM = 04, 01-09, 10-11-12
Month = April
Mon = Apr 

//Format of the day
DDD => 365 = 10-apr = 174 //The position of the day in the year 
DD => 30 = 10-apr = 10  //The position of the day in the month 
Day => Friday
Dy => Fri

FM to eliminate the blanks in the strings related to the date 
FMDay
Friday

//To_char function //is to convert a date to a string datatye (Varchar2)
Hire_date and sysdate (Date)
First_name, last_name (Varchar2) = String   

select to_char(sysdate, 'yyyy-mon-dy') fmt
from dual 
2020-Apr-Fri (Varchar2) = string

//Diplay the system date with everything spelled out 
select to_char(sysdate, 'DDSP "Of" Month Year')
from dual 
Tenth of april two thousand and twenty 

Table Student 
Social_sec_No (Varchar2) => string
'4563' = string

select to_number(Social_sec_No)
from student 

4563 => Number => int,float,double

//To_date function
converts strings to date according to a specific format

select to_date('95-05-240', 'yy-mm-ddd')
from dual 

'95-05-240' => String => 95-05-240 Date
 yy-mm-ddd
select sysdate 
from dual 

10-Apr-2020