Sql Query Automation?

HI All,

I want Automate rolling quarter logic permanently. We are loading the data every quarter and based upon billing date and paid updating the year value .Instead of adding new statement manually is there any way to automate this code for every quarter for ongoing process… and please check below sql and help me to automate the code

april 2

UPDATE TABLEASETYEAR= casewhen[b1].[BILLING_DATE]between'1/1/2013'and'12/31/2013'

           and[PAID_DATE]between'1/1/2013'and'3/31/2014' then'2013'

      when[b1].[BILLING_DATE]between'1/1/2010'and'12/31/2010'

          and[PAID_DATE]between'1/1/2010'and'3/31/2011' then'2010'

    when[b1].[BILLING_DATE]between'1/1/2011'and'12/31/2011'

        and[PAID_DATE]between'1/1/2011'and'3/31/2012' then'2011'

     when[b1].[BILLING_DATE]between'1/1/2012'and'12/31/2012'

        and[PAID_DATE]between'1/1/2012'and'3/31/2013' then'2012'        

        else'9999'end

WHEREyearis null

July 2

    UPDATE  TABLEASETYEAR=case

         when[b1].[BILLING_DATE]between'4/1/2013'and'3/31/2014'

           and[PAID_DATE]between'4/1/2013'and'6/30/2014' then'2013'

      when[b1].[BILLING_DATE]between'4/1/2010'and'3/31/2011'

          and[PAID_DATE]between'4/1/2010'and'6/30/2011' then'2010'

    when[b1].[BILLING_DATE]between'4/1/2011'and'3/31/2012'

        and[PAID_DATE]between'4/1/2011'and'6/30/2012' then'2011'

     when[b1].[BILLING_DATE]between'4/1/2012'and'3/31/2013'

        and[PAID_DATE]between'4/1/2012'and'6/30/2013' then'2012'        

        else'9999'end

WHEREyearis null

Oct 2

        UPDATE  TABLEASETYEAR=case

         when[b1].[BILLING_DATE]between'7/1/2013'and'6/30/2014'

           and[PAID_DATE]between'7/1/2013'and'9/30/2014' then'2014'

      when[b1].[BILLING_DATE]between'7/1/2010'and'6/30/2011'

          and[PAID_DATE]between'7/1/2010'and'9/30/2011' then'2011'

    when[b1].[BILLING_DATE]between'7/1/2011'and'6/30/2012'

        and[PAID_DATE]between'7/1/2011'and'9/30/2012' then'2012'

     when[b1].[BILLING_DATE]between'7/1/2012'and'6/30/2013'

        and[PAID_DATE]between'7/1/2012'and'9/30/2013' then'2013'        

        else'9999'end

WHEREyearis null

Jan 2

      UPDATE  TABLEASETYEAR=case

         when[b1].[BILLING_DATE]between'10/1/2013'and'9/30/2014'

           and[PAID_DATE]between'10/1/2013'and'12/31/2014' then'2014'

      when[b1].[BILLING_DATE]between'10/1/2010'and'9/30/2011'

          and[PAID_DATE]between'10/1/2010'and'12/31/2011' then'2011'

    when[b1].[BILLING_DATE]between'10/1/2011'and'9/30/2012'

        and[PAID_DATE]between'10/1/2011'and'12/31/2012' then'2012'

     when[b1].[BILLING_DATE]between'10/1/2012'and'9/30/2013'

        and[PAID_DATE]between'10/1/2012'and'12/31/2013' then'2013'        

        else'9999'end

WHEREyearis null

Thanks

CMK..