set @i=1
while @i<=4 begin
exec('update ??? set '+case when 1 then 'a1' when 2 then 'a2' when 3 then 'a3' else 'a4' end+' =???? where ????')
end
while @i<=4 begin
exec('update ??? set '+case when 1 then 'a1' when 2 then 'a2' when 3 then 'a3' else 'a4' end+' =???? where ????')
end
when 1 then 'a1'
when 2 then 'a2'
.........end?