Oracle删除重复记录的几种方式

原文链接：http://www.javaarch.net/jiagoushi/706.htm

Oracle删除重复记录的几种方式

如果把一个文件多次导入数据库，可能会引入重复记录，那么有哪些方法可以删除重复记录呢？

	REATE TABLE tbl_test(
		 SER_NO NUMBER,
		 FST_NM VARCHAR2(30),
		 DEPTID NUMBER,
		 CMNT   VARCHAR2(30));
	 
	INSERT INTO tbl_test VALUES(1, 'aaaaa', 2004, 'xxx');
	INSERT INTO tbl_test VALUES(2, 'bbbbb', 2005, 'yyy');
	INSERT INTO tbl_test VALUES(1, 'aaaaa', 2004, 'xxx');
	INSERT INTO tbl_test VALUES(1, 'aaaaa', 2004, 'xxx');
	INSERT INTO tbl_test VALUES(3, 'ccccc', 2005, 'zzz');
	INSERT INTO tbl_test VALUES(2, 'bbbbb', 2005, 'yyy');
	
1.Using MIN(rowid) 最常用的方法，但是数据量大的话执行会很长时间
	
	DELETE FROM tbl_test
		  WHERE ROWID NOT IN (SELECT   MIN (ROWID)
								  FROM tbl_test
							  GROUP BY ser_no, fst_nm, deptid, cmnt);
							  
2.Using MIN(rowid) & Join 跟第一条差不多

	DELETE FROM tbl_test t
		  WHERE t.ROWID NOT IN (SELECT MIN (b.ROWID)
								  FROM tbl_test b
								 WHERE b.ser_no = t.ser_no
								   AND b.fst_nm = t.fst_nm
								   AND b.deptid = t.deptid
								   AND b.cmnt   = t.cmnt);
								   
3.Using Subquery

	DELETE FROM tbl_test
	WHERE ser_no IN (SELECT ser_no FROM tbl_test GROUP BY ser_no, fst_nm, deptid, cmnt HAVING COUNT (*) > 1)
	AND fst_nm IN (SELECT fst_nm FROM tbl_test GROUP BY ser_no, fst_nm, deptid, cmnt HAVING COUNT (*) > 1)
	AND deptid IN (SELECT deptid FROM tbl_test GROUP BY ser_no, fst_nm, deptid, cmnt HAVING COUNT (*) > 1)
	AND cmnt   IN (SELECT cmnt   FROM tbl_test GROUP BY ser_no, fst_nm, deptid, cmnt HAVING COUNT (*) > 1)
	AND ROWID NOT IN (SELECT   MIN (ROWID) 
	FROM tbl_test
    GROUP BY ser_no, fst_nm, deptid, cmnt
	HAVING COUNT (*) > 1)							   
								
4. Using Nested Subqueries						

	DELETE FROM tbl_test a WHERE (a.ser_no, a.fst_nm, a.deptid, a.cmnt) IN (SELECT b.ser_no, b.fst_nm, b.deptid, b.cmnt
	FROM tbl_test b WHERE a.ser_no = b.ser_no AND a.fst_nm = b.fst_nm AND a.deptid = b.deptid AND a.cmnt  = b.cmnt AND 
	a.ROWID  > b.ROWID);
														  
5. Using Analytic Fucntions: 对于大表这是最有效的方法

	DELETE FROM tbl_test WHERE ROWID IN (SELECT rid FROM (SELECT ROWID rid,
	ROW_NUMBER () OVER (PARTITION BY ser_no, fst_nm, deptid, cmnt ORDER BY ROWID) rn FROM tbl_test)WHERE rn <> 1);													  
					
6. CREATE-DROP-RENAME 对资源使用比较合理，特别对于大表。但是如果需要回滚则会产生大量undo日志信息。
   
	CREATE  TABLE tbl_test1 NOLOGGING AS SELECT tbl_test .*
	FROM tbl_test tbl_test WHERE ROWID IN (SELECT rid 
	FROM (SELECT ROWID rid, ROW_NUMBER() OVER (PARTITION BY ser_no, fst_nm, deptid, cmnt ORDER BY ROWID) rn 
	FROM tbl_test) WHERE rn=1);
						 
	DROP TABLE tbl_test; --drop the original table with lots of duplicate	
	
	RENAME tbl_test1 TO tbl_test; -- your original table without duplicates.