SQL Delete duplicate data method

For example:
ID Name Value
1 a pp
2 a PP
3 B III
4 B pp
5 B pp
6 C pp
7 C pp
8 C III
ID is primary key
Ask for such a result
ID Name Value
1 a pp
3 B III
4 B pp
6 C pp
8 C III

Method 1
Delete yourtable
where [id] not in (
Select MAX ([id]) from yourtable
Group BY (name + value))

Method 2
Delete a
From Table a LEFT join (
Select Id=min (ID) from table GROUP by Name,value
) B on A.id=b.id
where b.id is null



SQL statement for querying and deleting duplicate records
SQL statement for querying and deleting 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)
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

(c)
Method One
Declare @max integer, @id integer
Declare cur_rows cursor Local for select main field, COUNT (*) from table name Group B Y main field has 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
Clo Se 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
)

SQL Delete duplicate data method