分组只保留一条数据
select min(KHID) from UCC_KHXX group by TEL
去除重复数据，只保留第一次录入的数据
DELETE FROM KHXX WHERE TEL IN
(select TEL from KHXX group by TEL having count(TEL) > 1)
and KHID not in(select min(KHID) from KHXX group by TEL having count(TEL)>1)