select * into #temp from tab where xxx=xxx;
update #temp set 主键=xxx where xxx=xxxx;(如果只有一条那么就不用where了)
insert into tab select * from #temp
下面语句挑出主键是123的数据,然后插入回原来的表,主键换成1234.
insert into tableName(pk, col1, col2...)
select 1234, col1, col2...
from tableName where pk = 123