One, query a field repeat
Copy Code code as follows:
SELECT *
From User u
where U.user_name in (select U.user_name
From User u
GROUP BY U.user_name has count (*) > 1)
Two, delete the duplicate of a few fields in the table
Example: There are six records in the table. Where John and Harry records are duplicated.
TableA
Copy Code code as follows:
ID Customer Phoneno
001 Sheets 3,777,777
002 Lee 4,444,444
003 King 5,555,555
004 Sheets 3,777,777
005 Sheets 3,777,777
006 King 5,555,555
How to write an SQL statement that turns TableA into the following
001 Sheets 3,777,777
002 Lee 4,444,444
003 King 5,555,555
Test environment
Copy Code code as follows:
CREATE TABLE TableA (ID varchar (3), Customer varchar (5), Phoneno varchar (6))
Insert INTO TableA Select ' 001 ', ' John ', ' 777777 '
UNION ALL SELECT ' 002 ', ' Dick ', ' 444444 '
UNION ALL SELECT ' 003 ', ' Harry ', ' 555555 '
UNION ALL SELECT ' 004 ', ' John ', ' 777777 '
UNION ALL SELECT ' 005 ', ' John ', ' 777777 '
UNION ALL SELECT ' 006 ', ' Harry ', ' 555555 '
Results
Copy Code code as follows:
Delete TableA from TableA twhere
Exists
Select 1fromtablea where Customer=t.customer and Phoneno=t.phoneno
Andid < Tt.id
)
Summarize
This method is useful for having a field of self extensibility, for example, in this example: ID
Copy Code code as follows:
Delete table name from table name as Twhere
Exists
Select 1from table name where field a=t. field A and field b=t. Field B, (...)
and self-added < T. self-adding columns
)
third, query and delete the SQL statements for duplicate records
SQL statements for querying and deleting duplicate records
1, look for redundant records in the table, duplicate records are based on a single field (Peopleid) to judge
Copy Code code as follows:
SELECT * from People
where Peopleid in (select Peopleid from People GROUP by Peopleid has count (Peopleid) > 1)
2, delete redundant records in the table, duplicate records are based on a single field (Peopleid) to judge, leaving only rowid minimal records
Copy Code code as follows:
Delete from people
where Peopleid in (select Peopleid from People GROUP by Peopleid has count (Peopleid) > 1)
and rowID not in (select min (rowid) from people GROUP by Peopleid have Count (Peopleid) >1)
Note: rowID for Oracle self-band ...
3. Find redundant records in the table (multiple fields)
Copy Code code 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 redundant records in the table (multiple fields), leaving only the smallest ROWID records
Copy Code code 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, look for redundant records in the table (multiple fields), does not contain the smallest ROWID records
Copy Code code 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
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;
Copy Code code as follows:
Select Name,count (*) from-A Group by Name has Count (*) > 1
If the same gender is also the same large as the following:
Copy Code code as follows:
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
)
