Various sql Finction

1.How to calculate age

SELECT DATEDIFF(DD,'1981-01-05 00:00:00.000',GETDATE())/365 AS AGE

2.How to calulate first day of previous month
select DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE())-1, 0)

Here 0 indicate as default date of sql(01/01/1900)

3. How to calculate last day of previous month

SELECT GETDATE()-DATEPART(dd,GETDATE())