SQL statement queries multiple fields in the same table duplicate records SQL database duplicate record delete

Share the following method of deleting duplicate records in a database with an SQL statement.
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
Select p1.* from Persons p1,persons P2 where p1.id<>p2.id and P1.cardid = P2.cardid and P1.pname = P2.pname and p1.a ddress = 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:
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;

The method of querying and deleting duplicate records. Reference Links:

• How do SQL statements remove duplicate records? Four different methods
• How do SQL statements remove duplicate records? Tutorials

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)

Two
Say
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

Three
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 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)

Four
Duplicate query
SELECT * FROM tablename where ID in (
Select ID from tablename
GROUP BY ID
Having count (ID) > 1
)
The following methods of operation may also be helpful:

• MSSQL SQL database Delete duplicate record SQL statement Daquan
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• MSSQL Delete duplicate record of SQL statement instance fine solution
• MSSQL SQL Database Delete duplicate Record Method Example
• MSSQL Delete database duplicate record SQL statement share