sql 判断表数据是否存在，然而进行修改新增

declare @AlyID int
select @AlyID=AlyID from tableA WHERE comid=1 --查看表是否存在数据
if isnull(@AlyID,'')!='' and @AlyID !='' --存在数据，进行修改
begin
UPDATE tableA SET columnA='' WHERE columnA =1  --修改
SELECT @AlyID as AlyID
END
ELSE
begin
insert into tableA( )values( )   --新增
select @@identity as AlyID     --得到自增ID
END