SQL query duplicate record-reprint

Suppose you have a table of people (table name: person), if you want to name, ID number, address the three fields exactly the same records to find out, using

   1:  SELECT p1.*   

   2: From  persons   p1,persons   p2   

   3:  WHERE p1.id<>p2.id   

   4: And  p1.cardid   =   p2.cardid   

   5: And  p1.pname   =   p2.pname   

   6: And  p1.address   =   p2.address

This functionality can be implemented.

SQL statement to delete duplicate records

1. Using the rowID method

2. Using the group by method

3. Using the Distinct method

1. Using the rowID method

According to the ROWID attribute of the Oracle band, it is judged whether there are duplicates, as follows:
Check the data:
SELECT * FROM table1 a where rowid! = (select Max (ROWID)
From table1 b where a.name1=b.name1 and a.name2=b.name2 ...)
Delete data:
Delete from table1 a where rowid! = (select Max (ROWID)
From table1 b where a.name1=b.name1 and a.name2=b.name2 ...)

2.group by method

Check the data:
Select COUNT (num), max (name) from student--Lists the number of duplicate records and lists his Name property
GROUP BY Num
Having count (num) >1--grouped by Num to find duplicates of num columns in a table that occur more than once
Delete data:
Delete from student
GROUP BY Num
Having count (num) >1
In this case, all the duplicates are deleted.

3. Using the distinct method -useful for small tables

CREATE TABLE Table_new as SELECT DISTINCT * FROM table1 Minux
TRUNCATE TABLE table1;
INSERT INTO table1 select * from Table_new;

how to query and delete duplicate records
1, look for redundant records in the table, duplicate records are based on a single field (Peopleid) to determine

SELECT * from People
where Peopleid in (select Peopleid from People GROUP by Peopleid have count (Peopleid) > 1)

2, delete redundant records in the table, duplicate records are based on a single field (Peopleid) to judge, leaving only the smallest ROWID records
Delete from people
where Peopleid in (select Peopleid from People GROUP by Peopleid have count (Peopleid) > 1)
and rowID not in (select min (rowid) from people GROUP by Peopleid have Count (Peopleid) >1)

3. Find redundant duplicate records (multiple fields) in the table
SELECT * FROM Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)

4. Delete extra duplicate records (multiple fields) in the table, leaving only the record with ROWID minimum
Delete from Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)
and rowID not in (select min (rowid) from Vitae GROUP by PEOPLEID,SEQ have Count (*) >1)

5. Find redundant duplicate records (multiple fields) in the table, not including the smallest ROWID records
SELECT * FROM Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)
and rowID not in (select min (rowid) from Vitae GROUP by PEOPLEID,SEQ have Count (*) >1)

(b) For example, a field "name" exists in table A,
and the "name" value may be the same between different records,
Now is the need to query out the records in the table, "name" value has duplicate entries;
Select Name,count (*) from A Group by Name have Count (*) > 1

If you also look at the same gender, the following is true:
Select Name,sex,count (*) from A Group by Name,sex have Count (*) > 1

(iii) method I

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 Two

Duplicate records have two meanings of duplicate records, one is a completely duplicate record, that is, all fields are duplicated records, second, some key fields duplicate records, such as the Name field is repeated, and the other fields may not be repeated or repeated can be ignored.

1, for the first kind of repetition, easier to solve, using

SELECT DISTINCT * from TableName

You can get a result set with no duplicate records.

If the table needs to delete duplicate records (duplicate records retain 1), you can delete them as follows

SELECT DISTINCT * to #Tmp from TableName

drop table TableName

SELECT * Into TableName from #Tmp

drop table #Tmp

This duplication occurs because the table is poorly designed and the unique index columns are added to resolve.

2, this kind of repetition problem usually requires to keep the first record in the duplicate record, the operation method is as follows

Suppose there is a duplicate field name,address, which requires the result set to be unique 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 on (select Autoid from #tmp2)

The last select is the result set that name,address not duplicate (but one more autoid field, which can be written in the SELECT clause without this column in the actual write)

(iv) Duplication of queries

SELECT * FROM tablename where ID in (

Select ID from tablename

GROUP BY ID

Having count (ID) > 1)

SQL query duplicate record-reprint