SQL statements for querying and deleting duplicate records

SQL statements for querying and deleting duplicate records

A)
For
There is a field "name" in Table A,
and the "name" value may be the same between different records,
Now you need to query the records in the table, the "name" value duplicates the item;

Select Name,count (*) from-a group by name has count (*) > 1
If the same gender is also the same large as the following:
Select Name,sex,count (*) from-a group by Name,sex have count (*) > 1

Two)
Method One

Declare @max integer, @id integer
Declare cur_rows cursor Local for select main field, COUNT (*) from table name Group by main field having count (*) >; 1
Open Cur_rows
Fetch cur_rows into @id, @max
While @ @fetch_status =0
Begin
Select @max = @max-1
SET ROWCOUNT @max
Delete from table name where main field = @id
Fetch cur_rows into @id, @max
End
Close Cur_rows
Set ROWCOUNT 0 method three

The duplicate record on, one is a completely duplicate record, that is, all the fields are duplicate records, the second is a number of key fields duplicate records, such as the Name field repeats, and other fields do not necessarily repeat or repeat can be ignored.
1, for the first duplication, easier to solve, using
SELECT DISTINCT * FROM tablename
You can get a result set without duplicate records.
If the table needs to delete duplicate records (1 for Duplicate records), you can delete them as follows
SELECT DISTINCT * into #tmp tablename
DROP TABLE TableName
SELECT * INTO TableName from #tmp
drop table #tmp
This duplication occurs because the table is poorly designed and can be resolved by adding a unique index column.
2. This type of repetition usually requires the first record in the duplicate record to be retained, as follows
Suppose there is a duplicate field of name,address that requires a unique result set for both fields
Select Identity (int,1,1) as Autoid, * into #tmp from TableName
Select min (autoid) as autoid into #tmp2 from #tmp Group by name,autoid
SELECT * from #tmp where autoid in (select Autoid from #tmp2)
The last select gets the name,address result set (but one more autoid field, which can be written in the SELECT clause to omit this column)

Method Four
Query duplication
SELECT * FROM tablename where ID in (
Select ID from tablename
GROUP BY ID
Having count (ID) > 1
)

SQL for some time, I found a lot of duplicate records in the table I built to test (not indexed). Later, we summarized some ways to delete duplicate records, in Oracle, you can delete duplicate records through unique ROWID, and you can also build temporary tables to implement ... This only refers to a few of the simple and practical methods, I hope to share with you (take the table employee as an example).

Sql> DESC Employee

Name NULL type
----------------------------------------- -------- ------------------

emp_id Number (10)
Emp_name VARCHAR2 (20)

Salary Number (10,2)

You can query for duplicate records in the following statement:

Sql> SELECT * from employee;

emp_id Emp_name Salary

---------- ---------------------------------------- ----------

1 Sunshine 10000

1 Sunshine 10000

2 Semon 20000

2 Semon 20000

3 xyz 30000

2 Semon 20000

Sql> SELECT DISTINCT * from employee;

emp_id Emp_name Salary

---------- ---------------------------------------- ----------

1 Sunshine 10000

2 Semon 20000

3 xyz 30000

Sql> SELECT * FROM Employee GROUP BY Emp_id,emp_name,salary has count (*) >1

emp_id Emp_name Salary

---------- ---------------------------------------- ----------

1 Sunshine 10000

2 Semon 20000

Sql> SELECT * FROM Employee E1

where rowID in (select Max (ROWID) from Employe E2
where e1.emp_id=e2.emp_id and

E1.emp_name=e2.emp_name and E1.salary=e2.salary);

emp_id Emp_name Salary

---------- ---------------------------------------- ----------

1 Sunshine 10000

3 xyz 30000

2 Semon 20000

Added

1, find redundant records in the table, duplicate records are judged by a single field (Peopleid)
Select * from arranges
where Peopleid in (select Peopleid from arranges GROUP BY Peopleid have count (Peopleid) > 1)
2, delete redundant records in a table, and duplicate records are judged by a single field (Peopleid), leaving only the ROWID minimal records
Delete From arranges
where Peopleid in (select Peopleid to arranges group by Peopleid has count (Peopleid) > 1)
and ROWID Not in (select min (rowid) from arranges group by Peopleid has count (Peopleid) >1)
3, lookup table redundant records (multiple fields)
SELECT * From Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq to Vitae GROUP by PEOPLEID,SEQ has count (*) > 1)
4, delete redundant records in the table (multiple fields), leaving only the smallest rowID records
Delete from Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from vitae GROUP BY PEOPLEID,SEQ has count (*) > 1)
and rowID not in (select min (rowid) from Vitae GROUP by Peopleid,seq having COUNT (*) >1)

5, find redundant records in the table (multiple fields), not including ROWID minimum records
SELECT * from Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP BY PEOPLEID,SEQ has count (*) > 1)