Using SQL statement or SQL Query to calculating the Number of Days in a Month
select datepart(dd,dateadd(dd,-1,dateadd(mm,1,cast(cast(year(getdate()) as varchar)+'-'+cast(month(getdate()) as varchar)+'-01' as datetime))))
Example on may(month), you just copy and paste the SQL Query or SQL statement (Above blue color) to the SQL Query Analyzer. You will get the answer is 31 days for May(month).