SQL

1、删除数据库中重复的数据并保留一条：

delete FROM T_TAG where TAGNAME in 
(SELECT TAGNAME from T_TAG GROUP BY TAGNAME HAVING count(TAGNAME) > 1) 
and TAGID not in 
(SELECT MIN(TAGID) from T_TAG GROUP BY TAGNAME HAVING count(TAGNAME) > 1);