SQL statements for querying and deleting duplicate records
1, look for redundant records in the table, duplicate records are based on a single field (ID) to judge
SELECT * FROM table where ID in (select Id from table GROUP by ID have count (Id) > 1)
2, delete redundant records in the table, duplicate records are based on a single field (ID) to judge, leaving only the smallest ROWID records
DELETE from table WHERE (ID) in (SELECT ID from table GROUP by ID have COUNT (ID) > 1) and ROWID not in (select MIN (ROWID) FR OM table GROUP by ID has COUNT (*) > 1);
3. Find redundant records in the table (multiple fields)
SELECT * FROM Table A
where (A.ID,A.SEQ) in (Select Id,seq from table group by ID,SEQ have count (*) > 1)
4, delete redundant records in the table (multiple fields), leaving only the smallest ROWID records
Delete from Table A
where (A.ID,A.SEQ) in (Select Id,seq from table group by ID,SEQ have count (*) > 1)
and rowID not in (select min (rowid) from table group by ID,SEQ have Count (*) >1)
5, look for redundant records in the table (multiple fields), does not contain the smallest ROWID records
SELECT * FROM Table A
where (A.ID,A.SEQ) in (Select Id,seq from table group by ID,SEQ have count (*) > 1)
and rowID not in (select min (rowid) from table group by ID,SEQ have Count (*) >1)
(b)
Say
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
Three
Method One
Copy Code code 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 record" has two duplicate records, one is a completely duplicate record, that is, all the fields are duplicate records, the second is a part of key fields duplicate records, such as the Name field repeat, and other fields do not necessarily repeat or repeat can be ignored.
1, for the first repetition, easier to solve, the use of
SELECT DISTINCT * FROM tablename
You can get a result set without duplicate records.
If the table needs to delete duplicate records (1 of duplicate records are retained), you can delete them in the following ways
Copy Code code 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
Copy Code code 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 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)
Four
Query duplication
Copy Code code as follows:
SELECT * FROM tablename where ID in (
Select ID from tablename
GROUP BY ID
Having count (ID) > 1
)
