1. SQL Dates
FdSc in ICT

2. Data and time functions
Usage
Purpose
HOUR()
HOUR(column)
Returns the hour value of a stored date
MINUTE()
MINUTE(column)
Returns the minute value of a stored date
SECOND()
SECOND(column)
Returns the second value of a stored date
DAYNAME()
DAYNAME(column)
Returns the name of the day of a stored date
DAYOFMONTH()
DAYOF MONTH(column)
Returns the numerical day value of a stored date
MONTHNAME()
MONTHNAME(column)
Returns the name of the month of a stored date
MONTH()
MONTH(column)
Returns the numerical month value of a stored date
YEAR()
YEAR(column)
Returns the year value of a stored date
ADDDATE()
ADDDATE(column, INTERVAL x type)
Returns the value of x units added to column
SUBDATE()
SUBDATE(column, INTERVAL x type)
Returns the value of x units subtracted from column
CURDATE()
Returns the current date
CURTIME()
Returns the current time
NOW()
Returns the current date and time

3. Obtaining the date and time
SQL
Result
SELECT curdate( )
SELECT curtime( )
20:58:08
SELECT now( )
:59:09

4. Selection
SQL
Result
SELECT name from dateexample where month (dateofbirth) = 7
Batman
SELECT dayname(dateofbirth) from dateexample where name = "Robin"
Wednesday

5. Age (in this example curdate is 2009-02-05)
SELECT YEAR(curdate()) - YEAR(DateOfBirth)
- (RIGHT(curdate(),5)<RIGHT(DateOfBirth,5))
AS age from dateexample
WHERE name = "Batman“
Analysis:
YEAR(curdate()) - YEAR(DateOfBirth) subtracts 1935 from 2009 giving 74
But this is incorrect as Batman will not be 74 until July 24.
So RIGHT(Curdate(),5) evaluates to (the first 5 characters from the right side of the current date) and RIGHT(DateOfBirth,5) evaluates to 07-24
02-05 is less than which evaluates to TRUE or 1
So the expression simplifies to 2009 – 1935 – 1 = 73

6. Age (in this example curdate is 2009-02-05)
SQL
Result
SELECT name, YEAR(curdate()) - YEAR(DateOfBirth)
- (RIGHT(curdate(),5)<RIGHT(DateOfBirth,5))
AS age from dateexample

7. Alias (in this example curdate is 2009-02-05)
An alias can be used to make headings and queries more succinct
SQL
Result
SELECT name, YEAR(curdate()) - YEAR(DateOfBirth)
- (RIGHT(curdate(),5)<RIGHT(DateOfBirth,5))
AS age from dateexample
(RIGHT(curdate(),5)<RIGHT(DateOfBirth,5))
from dateexample

8. Date calculations SQL Result SELECT curdate() 2009-02-06
WRONG!
SELECT adddate(curdate(), interval 2 day)
SELECT adddate(curdate(), interval 2 month)
SELECT subdate(curdate(), interval 2 month)