问题
I have the below table with the below records in it
create table employee
(
EmpId number,
EmpName varchar2(10),
EmpSSN varchar2(11)
);
insert into employee values(1, 'Jack', '555-55-5555');
insert into employee values (2, 'Joe', '555-56-5555');
insert into employee values (3, 'Fred', '555-57-5555');
insert into employee values (4, 'Mike', '555-58-5555');
insert into employee values (5, 'Cathy', '555-59-5555');
insert into employee values (6, 'Lisa', '555-70-5555');
insert into employee values (1, 'Jack', '555-55-5555');
insert into employee values (4, 'Mike', '555-58-5555');
insert into employee values (5, 'Cathy', '555-59-5555');
insert into employee values (6 ,'Lisa', '555-70-5555');
insert into employee values (5, 'Cathy', '555-59-5555');
insert into employee values (6, 'Lisa', '555-70-5555');
I dont have any primary key in this table .But i have the above records in my table already. I want to remove the duplicate records which has the same value in EmpId and EmpSSN fields.
Ex : Emp id 5
Can any one help me to frame a query to delete those duplicate records
Thanks in advance
回答1:
Add a Primary Key (code below)
Run the correct delete (code below)
Consider WHY you woudln't want to keep that primary key.
Assuming MSSQL or compatible:
ALTER TABLE Employee ADD EmployeeID int identity(1,1) PRIMARY KEY;
WHILE EXISTS (SELECT COUNT(*) FROM Employee GROUP BY EmpID, EmpSSN HAVING COUNT(*) > 1)
BEGIN
DELETE FROM Employee WHERE EmployeeID IN
(
SELECT MIN(EmployeeID) as [DeleteID]
FROM Employee
GROUP BY EmpID, EmpSSN
HAVING COUNT(*) > 1
)
END
回答2:
It is very simple. I tried in SQL Server 2008
DELETE SUB FROM
(SELECT ROW_NUMBER() OVER (PARTITION BY EmpId, EmpName, EmpSSN ORDER BY EmpId) cnt
FROM Employee) SUB
WHERE SUB.cnt > 1
回答3:
Use the row number to differentiate between duplicate records. Keep the first row number for an EmpID/EmpSSN and delete the rest:
DELETE FROM Employee a
WHERE ROW_NUMBER() <> ( SELECT MIN( ROW_NUMBER() )
FROM Employee b
WHERE a.EmpID = b.EmpID
AND a.EmpSSN = b.EmpSSN )
回答4:
With duplicates
As
(Select *, ROW_NUMBER() Over (PARTITION by EmpID,EmpSSN Order by EmpID,EmpSSN) as Duplicate From Employee)
delete From duplicates
Where Duplicate > 1 ;
This will update Table and remove all duplicates from the Table!
回答5:
select distinct * into newtablename from oldtablename
Now, the newtablename will have no duplicate records.
Simply change the table name(newtablename) by pressing F2 in object explorer in sql server.
回答6:
You could create a temporary table #tempemployee containing a select distinct of your employee table.
Then delete from employee.
Then insert into employee select from #tempemployee.
Like Josh said - even if you know the duplicates, deleting them will be impossile since you cannot actually refer to a specific record if it is an exact duplicate of another record.
回答7:
Code
DELETE DUP
FROM
(
SELECT ROW_NUMBER() OVER (PARTITION BY Clientid ORDER BY Clientid ) AS Val
FROM ClientMaster
) DUP
WHERE DUP.Val > 1
Explanation
Use an inner query to construct a view over the table which includes a field based on Row_Number(), partitioned by those columns you wish to be unique.
Delete from the results of this inner query, selecting anything which does not have a row number of 1; i.e. the duplicates; not the original.
The order by clause of the row_number window function is needed for a valid syntax; you can put any column name here. If you wish to change which of the results is treated as a duplicate (e.g. keep the earliest or most recent, etc), then the column(s) used here do matter; i.e. you want to specify the order such that the record you wish to keep will come first in the result.
回答8:
If you don't want to create a new primary key you can use the TOP command in SQL Server:
declare @ID int
while EXISTS(select count(*) from Employee group by EmpId having count(*)> 1)
begin
select top 1 @ID = EmpId
from Employee
group by EmpId
having count(*) > 1
DELETE TOP(1) FROM Employee WHERE EmpId = @ID
end
回答9:
ITS easy use below query
WITH Dups AS
(
SELECT col1,col2,col3,
ROW_NUMBER() OVER(PARTITION BY col1,col2,col3 ORDER BY (SELECT 0)) AS rn
FROM mytable
)
DELETE FROM Dups WHERE rn > 1
回答10:
delete sub from (select ROW_NUMBER() OVer(Partition by empid order by empid)cnt from employee)sub where sub.cnt>1
回答11:
I'm not an SQL expert so bear with me. I'm sure you'll get a better answer soon enough. Here's how you can find the duplicate records.
select t1.empid, t1.empssn, count(*)
from employee as t1
inner join employee as t2 on (t1.empid=t2.empid and t1.empssn = t2.empssn)
group by t1.empid, t1.empssn
having count(*) > 1
Deleting them will be more tricky because there is nothing in the data that you could use in a delete statement to differentiate the duplicates. I suspect the answer will involve row_number() or adding an identity column.
回答12:
create unique clustered index Employee_idx on Employee ( EmpId,EmpSSN ) with ignore_dup_key
You can drop the index if you don't need it.
回答13:
no ID, no rowcount() or no temp table needed....
WHILE
(
SELECT COUNT(*)
FROM TBLEMP
WHERE EMPNO
IN (SELECT empno from tblemp group by empno having count(empno)>1)) > 1
DELETE top(1)
FROM TBLEMP
WHERE EMPNO IN (SELECT empno from tblemp group by empno having count(empno)>1)
回答14:
there are two columns in the a table ID and name where names are repeating with different IDs so for that you may use this query: . .
DELETE FROM dbo.tbl1
WHERE id NOT IN (
Select MIN(Id) AS namecount FROM tbl1
GROUP BY Name
)
回答15:
Having a database table without Primary Key is really and will say extremely BAD PRACTICE...so after you add one (ALTER TABLE)
Run this until you don't see any more duplicated records (that is the purpose of HAVING COUNT)
DELETE FROM [TABLE_NAME] WHERE [Id] IN
(
SELECT MAX([Id])
FROM [TABLE_NAME]
GROUP BY [TARGET_COLUMN]
HAVING COUNT(*) > 1
)
SELECT MAX([Id]),[TABLE_NAME], COUNT(*) AS dupeCount
FROM [TABLE_NAME]
GROUP BY [TABLE_NAME]
HAVING COUNT(*) > 1
MAX([Id]) will cause to delete latest records (ones added after first created) in case you want the opposite meaning that in case of requiring deleting first records and leave the last record inserted please use MIN([Id])
回答16:
select t1.* from employee t1, employee t2 where t1.empid=t2.empid and t1.empname = t2.empname and t1.salary = t2.salary
group by t1.empid, t1.empname,t1.salary having count(*) > 1
回答17:
DELETE FROM 'test'
USING 'test' , 'test' as vtable
WHERE test.id>vtable.id and test.common_column=vtable.common_column
Using this we can remove duplicate records
回答18:
ALTER IGNORE TABLE test
ADD UNIQUE INDEX 'test' ('b');
@ here 'b' is column name to uniqueness, @ here 'test' is index name.
来源：https://stackoverflow.com/questions/985384/delete-duplicate-records-from-a-sql-table-without-a-primary-key