## 1.需求说明
TEST表情况说明：

- 按月进行分区的分区表 	
 - 未定义主键或唯一索引 	
 - 包含COL1,COL2,COL3,INSERTTIME四列

现需要删除2019年3月31日当天存在的重复数据

## 2.解决方法
### 2.1 确认无重复数据的记录数
```sql
SELECT COUNT(1) FROM (
	SELECT COL1,COL2,COL3,INSERTTIME FROM TEST PARTITION(P201903) A 
		WHERE INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01'
		GROUP BY COL1,COL2,COL3
);
```

### 2.2 梳理需要筛选的数据
由于原表A数据量特别大，此处新建一张表将需要处理的数据单独存放

```sql
CREATE TABLE TEST_TMP NOLOGGING AS
SELECT /*PARALLEL +8 */ A.*,A.ROWID ROWID_OLD FROM TEST PARTITION(P201903) A 
	WHERE INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01';
```

### 2.2 确认需要删除的数据
理论上而言需要删除和需要保留的数据记录数应相等
```sql
--需要删除的数据记录数	
SELECT COUNT(1) FROM TEST PARTITION(P201903) A WHERE ROWID IN (
	SELECT MIN(ROWID_OLD) ROWID_OLD FROM TEST_TMP 
	WHERE INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01' 
	GROUP BY COL1,COL2,COL3,INSERTTIME 
	HAVING COUNT(1) > 1)
AND INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01'

--需要保留的数据记录数	
SELECT COUNT(1) FROM TEST PARTITION(P201903) A WHERE ROWID NOT IN (
	SELECT MIN(ROWID_OLD) ROWID_OLD FROM TEST_TMP 
	WHERE INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01' 
	GROUP BY COL1,COL2,COL3,INSERTTIME 
	HAVING COUNT(1) > 1)
AND INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01'
```

### 2.3 利用分批提交删除重复数据
```sql
DECLARE
      TYPE ROWID_LIST IS TABLE OF UROWID INDEX BY BINARY_INTEGER;
      ROWID_INFOS ROWID_LIST;
      I NUMBER;
      CURSOR C_ROWIDS IS  (SELECT MIN(ROWID_OLD) ROWID_OLD
                            FROM TEST_TMP 
                           WHERE INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01' 
                           GROUP BY  COL1,COL2,COL3,INSERTTIME
                           HAVING COUNT(1) > 1);
  BEGIN
      OPEN C_ROWIDS;
   
      LOOP
      --此处LIMIT后的值为分批提交的记录数，可以根据实际情况调整
       FETCH C_ROWIDS BULK COLLECT INTO ROWID_INFOS LIMIT 10000;
  
       FORALL I IN 1..ROWID_INFOS.COUNT
        --如下的DELETE语句为分批提交实际需要执行的部分
        DELETE FROM TEST WHERE ROWID=ROWID_INFOS(I);

COMMIT;
       EXIT WHEN ROWID_INFOS.COUNT<10000;
    END LOOP;
    CLOSE C_ROWIDS;
 END;
```
### 2.4 确认无重复数据

```sql
SELECT * FROM (
	SELECT COL1,COL2,COL3,INSERTTIME FROM TEST PARTITION(P201903) A 
		WHERE INSERTTIME >= DATE'2019-03-31' AND INSERTTIME < DATE'2019-04-01'
		GROUP BY COL1,COL2,COL3,INSERTTIME
		HAVING COUNT(1)>1 )
);
```

ITPub博客

ORACLE批量删除无主键重复数据

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