--First Day of the Current Month

SELECT DATEADD(MM, datediff(MM, 0, getdate()), 0)

​

--Last Day of the Current Month

SELECT DATEADD(DD, -1, DATEADD(MM, DATEDIFF(MM, 0, GETDATE()) + 1, 0))

​

--First Day of the Previous Month

SELECT DATEADD(MM, DATEDIFF(MM, 0, GETDATE()) - 1, 0)

​

--Last Day of the Previous Month

SELECT CONVERT(DATETIME,CONVERT(DATE,DATEADD(DD, -(DAY(GETDATE())), GETDATE())))

​

--First Day of the Next Month

SELECT DATEADD(MM, DATEDIFF(MM, 0, GETDATE()) + 1, 0)

​

--Last Day of the Next Month

SELECT DATEADD (DD, -1, DATEADD(MM, DATEDIFF(MM, 0, GETDATE()) + 2, 0))

SELECT DATEADD(yy, DATEDIFF(yy, 0, GETDATE()), 0);          -- SQL Server

SELECT TRUNC(sysdate, 'YEAR') FROM DUAL;                    -- Oracle

SELECT MAKEDATE(year(now()), 1);                            -- MySQL