LAST_DAY() Last Day of the month in MySQL Query

SELECT LAST_DAY(  '2016-12-25' )
Output is 2016-12-31

Syntax of LAST_DAY() 
LAST_DAY(date)
DEMO: Select date from Calendar to execute LAST_DAY()

With datetime 
SELECT LAST_DAY('2016-09-13 12:59:45')
Output is 2016-09-30

We can use DATE_FORMAT() to change the output 
select DATE_FORMAT(LAST_DAY('2016-09-15'),'%W %D %M %Y')
Output is Friday 30th September 2016

What is the last date of current month? Now() returns the present date and time 
SELECT LAST_DAY( NOW( ) )

LAST DAY OF Previous Month

SELECT LAST_DAY(CURDATE() - INTERVAL 1 MONTH)

CURDATE() to get First day and last day of previous Month

Present Month Records

Starting from 1st day of the current month till now. ( there is no FAST_DAY() function to get the 1st day of the month). 
SELECT * FROM `dt_table` WHERE  date between  DATE_FORMAT(CURDATE() ,'%Y-%m-01') AND CURDATE()

Get the last working day of the month

Sunday is not a working day of the month, so to get the last working day of the month we have to use weekday() function and then use IF function to check condition to change the date by 1 if last_day() returns SUNDAY , to get the last working day of the month. 
SELECT IF( DAYOFWEEK( LAST_DAY( NOW( ) ) ) =1, DATE_ADD( LAST_DAY( NOW( ) ) , INTERVAL -1 DAY ) , LAST_DAY( NOW( ) ) )
Try this 
SELECT IF( DAYOFWEEK( LAST_DAY( '2016-07-20' ) ) =1, DATE_ADD( LAST_DAY( '2016-07-20' ) , INTERVAL -1 DAY ) , LAST_DAY( '2016-07-20' ) )
Output is 2016-07-30

Now let us try again the last date of current month.