mysql删除重复数据

DELETE FROM test WHERE id NOT IN (
SELECT id AS id FROM (
SELECT MIN(id) AS id #和外边的条件使用一样的名字
FROM test GROUP BY NAME
) AS t #嵌套出来的子查询都会生成一个派生表，而MYSQL规定派生表必须有一个别名
);

#删除重复记录
#通过使用rowid来作为过滤条件，性能高效
DELETE FROM emp e
WHERE  e.ROWID > (SELECT MIN( x.ROWID )
FROM   emp x
WHERE  x.empno = e.empno);