Three ways to remove duplicate records from Oracle queries

This article lists 3 ways to delete duplicate records, namely ROWID, group by and distinct, which can be consulted by small partners.

For example, there is now a person table (table name: peosons)
If you want to name, ID, address, the three fields exactly the same record query

The code is as follows: Select p1.*
From persons p1,persons P2
where p1.id<>p2.id
and P1.cardid = P2.cardid and P1.pname = p2.pname and p1.address = p2.address

Can achieve the above effect.

Several SQL statements that 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:

The code is as follows: SELECT * FROM table1 a where rowid! = (select Max (ROWID)
From table1 b where a.name1=b.name1 and a.name2=b.name2 ...)

Delete data:

The code is as follows: 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:

The code looks like this: 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:

The code is as follows: 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

The code is as follows: 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

The code is as follows: 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

The code is as follows: Delete from people
where Peopleid in (select Peopleid from people GROUP by Peopleid
Having 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

The code is as follows: 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

The code is as follows: 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

The code is as follows: 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)

Two

For example, there is a field "name" in Table A, and the "name" value between different records may be the same, now it is necessary to query out the records in the table, "name" value has duplicate entries;

The code is as follows: Select Name,count (*) from A Group by Name have Count (*) > 1

If you also look at the same gender, the following is true:

The code is as follows: Select Name,sex,count (*) from A Group by Name,sex have Count (*) > 1

Three

Method One

The code is as follows: 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 the fields are duplicates of the record, and the second is some key field duplicate records,
For example, the Name field is repeated, and the other fields are not necessarily repeated or can be omitted.

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

The code is as follows: 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

The code is as follows: SELECT DISTINCT * into #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

Copy CodeThe code is as follows: 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)

Four

Duplicate query

The code is as follows: SELECT * FROM tablename where ID in (
Select ID from tablename
GROUP BY ID
Having count (ID) > 1
)

Three ways to remove duplicate records from Oracle queries