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How can I delete duplicate rows where no unique row id exists?
My table is
col1 col2 col3 col4 col5 col6 col7
john 1 1 1 1 1 1
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
sally 2 2 2 2 2 2
I want to be left with the following after the duplicate removal:
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
I've tried a few queries but I think they depend on having a row id as I don't get the desired result. For example:
DELETE
FROM table
WHERE col1 IN (
SELECT id
FROM table
GROUP BY id
HAVING (COUNT(col1) > 1)
)
I like CTEs and ROW_NUMBER as the two combined allow us to see which rows are deleted (or updated), therefore just change the DELETE FROM CTE... to SELECT * FROM CTE:
WITH CTE AS(
SELECT [col1], [col2], [col3], [col4], [col5], [col6], [col7],
RN = ROW_NUMBER()OVER(PARTITION BY col1 ORDER BY col1)
FROM dbo.Table1
)
DELETE FROM CTE WHERE RN > 1
DEMO (result is different; I assume that it's due to a typo on your part)
COL1 COL2 COL3 COL4 COL5 COL6 COL7
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
This example determines duplicates by a single column col1 because of the PARTITION BY col1. If you want to include multiple columns simply add them to the PARTITION BY:
ROW_NUMBER()OVER(PARTITION BY Col1, Col2, ... ORDER BY OrderColumn)
I would prefer CTE for deleting duplicate rows from sql server table
strongly recommend to follow this article ::http://codaffection.com/sql-server-article/delete-duplicate-rows-in-sql-server/
by keeping original
WITH CTE AS
(
SELECT *,ROW_NUMBER() OVER (PARTITION BY col1,col2,col3 ORDER BY col1,col2,col3) AS RN
FROM MyTable
)
DELETE FROM CTE WHERE RN<>1
without keeping original
WITH CTE AS
(SELECT *,R=RANK() OVER (ORDER BY col1,col2,col3)
FROM MyTable)
DELETE CTE
WHERE R IN (SELECT R FROM CTE GROUP BY R HAVING COUNT(*)>1)
Without using CTE and ROW_NUMBER() you can just delete the records just by using group by with MAX function here is an example
DELETE
FROM MyDuplicateTable
WHERE ID NOT IN
(
SELECT MAX(ID)
FROM MyDuplicateTable
GROUP BY DuplicateColumn1, DuplicateColumn2, DuplicateColumn3)
If you have no references, like foreign keys, you can do this. I do it a lot when testing proofs of concept and the test data gets duplicated.
SELECT DISTINCT [col1],[col2],[col3],[col4],[col5],[col6],[col7]
INTO [newTable]
FROM [oldTable]
Go into the object explorer and delete the old table.
Rename the new table with the old table's name.
Remove all duplicates, but the very first ones (with min ID)
should work equally in other SQL servers, like Postgres:
DELETE FROM table
WHERE id NOT IN (
select min(id) from table
group by col1, col2, col3, col4, col5, col6, col7
)
DELETE from search
where id not in (
select min(id) from search
group by url
having count(*)=1
union
SELECT min(id) FROM search
group by url
having count(*) > 1
)
There are two solutions in mysql:
A) Delete duplicate rows using DELETE JOIN statement
DELETE t1 FROM contacts t1
INNER JOIN contacts t2
WHERE
t1.id < t2.id AND
t1.email = t2.email;
This query references the contacts table twice, therefore, it uses the table alias t1 and t2.
The output is:
1
Query OK, 4 rows affected (0.10 sec)
In case you want to delete duplicate rows and keep the lowest id, you can use the following statement:
DELETE c1 FROM contacts c1
INNER JOIN contacts c2
WHERE
c1.id > c2.id AND
c1.email = c2.email;
B) Delete duplicate rows using an intermediate table
The following shows the steps for removing duplicate rows using an intermediate table:
1. Create a new table with the structure the same as the original table that you want to delete duplicate rows.
2. Insert distinct rows from the original table to the immediate table.
3. Insert distinct rows from the original table to the immediate table.
Step 1. Create a new table whose structure is the same as the original table:
CREATE TABLE source_copy LIKE source;
Step 2. Insert distinct rows from the original table to the new table:
INSERT INTO source_copy
SELECT * FROM source
GROUP BY col; -- column that has duplicate values
Step 3. drop the original table and rename the immediate table to the original one
DROP TABLE source;
ALTER TABLE source_copy RENAME TO source;
Source: http://www.mysqltutorial.org/mysql-delete-duplicate-rows/
Please see the below way of deletion too.
Declare #table table
(col1 varchar(10),col2 int,col3 int, col4 int, col5 int, col6 int, col7 int)
Insert into #table values
('john',1,1,1,1,1,1),
('john',1,1,1,1,1,1),
('sally',2,2,2,2,2,2),
('sally',2,2,2,2,2,2)
Created a sample table named #table and loaded it with given data.
Delete aliasName from (
Select *,
ROW_NUMBER() over (Partition by col1,col2,col3,col4,col5,col6,col7 order by col1) as rowNumber
From #table) aliasName
Where rowNumber > 1
Select * from #table
Note: If you are giving all columns in the Partition by part, then order by do not have much significance.
I know, the question is asked three years ago, and my answer is another version of what Tim has posted, But posting just incase it is helpful for anyone.
It can be done by many ways in sql server
the most simplest way to do so is:
Insert the distinct rows from the duplicate rows table to new temporary table. Then delete all the data from duplicate rows table then insert all data from temporary table which has no duplicates as shown below.
select distinct * into #tmp From table
delete from table
insert into table
select * from #tmp drop table #tmp
select * from table
Delete duplicate rows using Common Table Expression(CTE)
With CTE_Duplicates as
(select id,name , row_number()
over(partition by id,name order by id,name ) rownumber from table )
delete from CTE_Duplicates where rownumber!=1
To delete the duplicate rows from the table in SQL Server, you follow these steps:
Find duplicate rows using GROUP BY clause or ROW_NUMBER() function.
Use DELETE statement to remove the duplicate rows.
Setting up a sample table
DROP TABLE IF EXISTS contacts;
CREATE TABLE contacts(
contact_id INT IDENTITY(1,1) PRIMARY KEY,
first_name NVARCHAR(100) NOT NULL,
last_name NVARCHAR(100) NOT NULL,
email NVARCHAR(255) NOT NULL,
);
Insert values
INSERT INTO contacts
(first_name,last_name,email)
VALUES
('Syed','Abbas','syed.abbas#example.com'),
('Catherine','Abel','catherine.abel#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Hazem','Abolrous','hazem.abolrous#example.com'),
('Hazem','Abolrous','hazem.abolrous#example.com'),
('Humberto','Acevedo','humberto.acevedo#example.com'),
('Humberto','Acevedo','humberto.acevedo#example.com'),
('Pilar','Ackerman','pilar.ackerman#example.com');
Query
SELECT
contact_id,
first_name,
last_name,
email
FROM
contacts;
Delete duplicate rows from a table
WITH cte AS (
SELECT
contact_id,
first_name,
last_name,
email,
ROW_NUMBER() OVER (
PARTITION BY
first_name,
last_name,
email
ORDER BY
first_name,
last_name,
email
) row_num
FROM
contacts
)
DELETE FROM cte
WHERE row_num > 1;
Should delete the record now
Try to Use:
SELECT linkorder
,Row_Number() OVER (
PARTITION BY linkorder ORDER BY linkorder DESC
) AS RowNum
FROM u_links
Microsoft has a vey ry neat guide on how to remove duplicates. Check out http://support.microsoft.com/kb/139444
In brief, here is the easiest way to delete duplicates when you have just a few rows to delete:
SET rowcount 1;
DELETE FROM t1 WHERE myprimarykey=1;
myprimarykey is the identifier for the row.
I set rowcount to 1 because I only had two rows that were duplicated. If I had had 3 rows duplicated then I would have set rowcount to 2 so that it deletes the first two that it sees and only leaves one in table t1.
with myCTE
as
(
select productName,ROW_NUMBER() over(PARTITION BY productName order by slno) as Duplicate from productDetails
)
Delete from myCTE where Duplicate>1
After trying the suggested solution above, that works for small medium tables.
I can suggest that solution for very large tables. since it runs in iterations.
Drop all dependency views of the LargeSourceTable
you can find the dependecies by using sql managment studio, right click on the table and click "View Dependencies"
Rename the table:
sp_rename 'LargeSourceTable', 'LargeSourceTable_Temp'; GO
Create the LargeSourceTable again, but now, add a primary key with all the columns that define the duplications add WITH (IGNORE_DUP_KEY = ON)
For example:
CREATE TABLE [dbo].[LargeSourceTable]
(
ID int IDENTITY(1,1),
[CreateDate] DATETIME CONSTRAINT [DF_LargeSourceTable_CreateDate] DEFAULT (getdate()) NOT NULL,
[Column1] CHAR (36) NOT NULL,
[Column2] NVARCHAR (100) NOT NULL,
[Column3] CHAR (36) NOT NULL,
PRIMARY KEY (Column1, Column2) WITH (IGNORE_DUP_KEY = ON)
);
GO
Create again the views that you dropped in the first place for the new created table
Now, Run the following sql script, you will see the results in 1,000,000 rows per page, you can change the row number per page to see the results more often.
Note, that I set the IDENTITY_INSERT on and off because one the columns contains auto incremental id, which I'm also copying
SET IDENTITY_INSERT LargeSourceTable ON
DECLARE #PageNumber AS INT, #RowspPage AS INT
DECLARE #TotalRows AS INT
declare #dt varchar(19)
SET #PageNumber = 0
SET #RowspPage = 1000000
select #TotalRows = count (*) from LargeSourceTable_TEMP
While ((#PageNumber - 1) * #RowspPage < #TotalRows )
Begin
begin transaction tran_inner
; with cte as
(
SELECT * FROM LargeSourceTable_TEMP ORDER BY ID
OFFSET ((#PageNumber) * #RowspPage) ROWS
FETCH NEXT #RowspPage ROWS ONLY
)
INSERT INTO LargeSourceTable
(
ID
,[CreateDate]
,[Column1]
,[Column2]
,[Column3]
)
select
ID
,[CreateDate]
,[Column1]
,[Column2]
,[Column3]
from cte
commit transaction tran_inner
PRINT 'Page: ' + convert(varchar(10), #PageNumber)
PRINT 'Transfered: ' + convert(varchar(20), #PageNumber * #RowspPage)
PRINT 'Of: ' + convert(varchar(20), #TotalRows)
SELECT #dt = convert(varchar(19), getdate(), 121)
RAISERROR('Inserted on: %s', 0, 1, #dt) WITH NOWAIT
SET #PageNumber = #PageNumber + 1
End
SET IDENTITY_INSERT LargeSourceTable OFF
-- this query will keep only one instance of a duplicate record.
;WITH cte
AS (SELECT ROW_NUMBER() OVER (PARTITION BY col1, col2, col3-- based on what? --can be multiple columns
ORDER BY ( SELECT 0)) RN
FROM Mytable)
delete FROM cte
WHERE RN > 1
You need to group by the duplicate records according to the field(s), then hold one of the records and delete the rest.
For example:
DELETE prg.Person WHERE Id IN (
SELECT dublicateRow.Id FROM
(
select MIN(Id) MinId, NationalCode
from prg.Person group by NationalCode having count(NationalCode ) > 1
) GroupSelect
JOIN prg.Person dublicateRow ON dublicateRow.NationalCode = GroupSelect.NationalCode
WHERE dublicateRow.Id <> GroupSelect.MinId)
Deleting duplicates from a huge(several millions of records) table might take long time . I suggest that you do a bulk insert into a temp table of the selected rows rather than deleting.
--REWRITING YOUR CODE(TAKE NOTE OF THE 3RD LINE) WITH CTE AS(SELECT NAME,ROW_NUMBER()
OVER (PARTITION BY NAME ORDER BY NAME) ID FROM #TB) SELECT * INTO #unique_records FROM
CTE WHERE ID =1;
This might help in your case
DELETE t1 FROM table t1 INNER JOIN table t2 WHERE t1.id > t2.id AND t1.col1 = t2.col1
With reference to https://support.microsoft.com/en-us/help/139444/how-to-remove-duplicate-rows-from-a-table-in-sql-server
The idea of removing duplicate involves
a) Protecting those rows that are not duplicate
b) Retain one of the many rows that qualified together as duplicate.
Step-by-step
1) First identify the rows those satisfy the definition of duplicate
and insert them into temp table, say #tableAll .
2) Select non-duplicate(single-rows) or distinct rows into temp table
say #tableUnique.
3) Delete from source table joining #tableAll to delete the
duplicates.
4) Insert into source table all the rows from #tableUnique.
5) Drop #tableAll and #tableUnique
If you have the ability to add a column to the table temporarily, this was a solution that worked for me:
ALTER TABLE dbo.DUPPEDTABLE ADD RowID INT NOT NULL IDENTITY(1,1)
Then perform a DELETE using a combination of MIN and GROUP BY
DELETE b
FROM dbo.DUPPEDTABLE b
WHERE b.RowID NOT IN (
SELECT MIN(RowID) AS RowID
FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
GROUP BY a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE
);
Verify that the DELETE performed correctly:
SELECT a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE, COUNT(*)--MIN(RowID) AS RowID
FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
GROUP BY a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE
ORDER BY COUNT(*) DESC
The result should have no rows with a count greater than 1. Finally, remove the rowid column:
ALTER TABLE dbo.DUPPEDTABLE DROP COLUMN RowID;
Oh wow, i feel so stupid by ready all this answers, they are like experts' answer with all CTE and temp table and etc.
And all I did to get it working was simply aggregated the ID column by using MAX.
DELETE FROM table WHERE col1 IN (
SELECT MAX(id) FROM table GROUP BY id HAVING ( COUNT(col1) > 1 )
)
NOTE: you might need to run it multiple time to remove duplicate as this will only delete one set of duplicate rows at a time.
please simply add the keyword DISTINCT right after the SELECT command,
for example:
SELECT DISTICNT ColumnOne, ColumnTwo, ColumnThree
FROM YourTable
Another way of removing dublicated rows without loosing information in one step is like following:
delete from dublicated_table t1 (nolock)
join (
select t2.dublicated_field
, min(len(t2.field_kept)) as min_field_kept
from dublicated_table t2 (nolock)
group by t2.dublicated_field having COUNT(*)>1
) t3
on t1.dublicated_field=t3.dublicated_field
and len(t1.field_kept)=t3.min_field_kept
DECLARE #TB TABLE(NAME VARCHAR(100));
INSERT INTO #TB VALUES ('Red'),('Red'),('Green'),('Blue'),('White'),('White')
--**Delete by Rank**
;WITH CTE AS(SELECT NAME,DENSE_RANK() OVER (PARTITION BY NAME ORDER BY NEWID()) ID FROM #TB)
DELETE FROM CTE WHERE ID>1
SELECT NAME FROM #TB;
--**Delete by Row Number**
;WITH CTE AS(SELECT NAME,ROW_NUMBER() OVER (PARTITION BY NAME ORDER BY NAME) ID FROM #TB)
DELETE FROM CTE WHERE ID>1;
SELECT NAME FROM #TB;
DELETE FROM TBL1 WHERE ID IN
(SELECT ID FROM TBL1 a WHERE ID!=
(select MAX(ID) from TBL1 where DUPVAL=a.DUPVAL
group by DUPVAL
having count(DUPVAL)>1))
DELETE p1 FROM Person p1,
Person p2
WHERE
p1.Email = p2.Email AND p1.Id > p2.Id
How can I delete duplicate rows where no unique row id exists?
My table is
col1 col2 col3 col4 col5 col6 col7
john 1 1 1 1 1 1
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
sally 2 2 2 2 2 2
I want to be left with the following after the duplicate removal:
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
I've tried a few queries but I think they depend on having a row id as I don't get the desired result. For example:
DELETE
FROM table
WHERE col1 IN (
SELECT id
FROM table
GROUP BY id
HAVING (COUNT(col1) > 1)
)
I like CTEs and ROW_NUMBER as the two combined allow us to see which rows are deleted (or updated), therefore just change the DELETE FROM CTE... to SELECT * FROM CTE:
WITH CTE AS(
SELECT [col1], [col2], [col3], [col4], [col5], [col6], [col7],
RN = ROW_NUMBER()OVER(PARTITION BY col1 ORDER BY col1)
FROM dbo.Table1
)
DELETE FROM CTE WHERE RN > 1
DEMO (result is different; I assume that it's due to a typo on your part)
COL1 COL2 COL3 COL4 COL5 COL6 COL7
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
This example determines duplicates by a single column col1 because of the PARTITION BY col1. If you want to include multiple columns simply add them to the PARTITION BY:
ROW_NUMBER()OVER(PARTITION BY Col1, Col2, ... ORDER BY OrderColumn)
I would prefer CTE for deleting duplicate rows from sql server table
strongly recommend to follow this article ::http://codaffection.com/sql-server-article/delete-duplicate-rows-in-sql-server/
by keeping original
WITH CTE AS
(
SELECT *,ROW_NUMBER() OVER (PARTITION BY col1,col2,col3 ORDER BY col1,col2,col3) AS RN
FROM MyTable
)
DELETE FROM CTE WHERE RN<>1
without keeping original
WITH CTE AS
(SELECT *,R=RANK() OVER (ORDER BY col1,col2,col3)
FROM MyTable)
DELETE CTE
WHERE R IN (SELECT R FROM CTE GROUP BY R HAVING COUNT(*)>1)
Without using CTE and ROW_NUMBER() you can just delete the records just by using group by with MAX function here is an example
DELETE
FROM MyDuplicateTable
WHERE ID NOT IN
(
SELECT MAX(ID)
FROM MyDuplicateTable
GROUP BY DuplicateColumn1, DuplicateColumn2, DuplicateColumn3)
If you have no references, like foreign keys, you can do this. I do it a lot when testing proofs of concept and the test data gets duplicated.
SELECT DISTINCT [col1],[col2],[col3],[col4],[col5],[col6],[col7]
INTO [newTable]
FROM [oldTable]
Go into the object explorer and delete the old table.
Rename the new table with the old table's name.
Remove all duplicates, but the very first ones (with min ID)
should work equally in other SQL servers, like Postgres:
DELETE FROM table
WHERE id NOT IN (
select min(id) from table
group by col1, col2, col3, col4, col5, col6, col7
)
DELETE from search
where id not in (
select min(id) from search
group by url
having count(*)=1
union
SELECT min(id) FROM search
group by url
having count(*) > 1
)
There are two solutions in mysql:
A) Delete duplicate rows using DELETE JOIN statement
DELETE t1 FROM contacts t1
INNER JOIN contacts t2
WHERE
t1.id < t2.id AND
t1.email = t2.email;
This query references the contacts table twice, therefore, it uses the table alias t1 and t2.
The output is:
1
Query OK, 4 rows affected (0.10 sec)
In case you want to delete duplicate rows and keep the lowest id, you can use the following statement:
DELETE c1 FROM contacts c1
INNER JOIN contacts c2
WHERE
c1.id > c2.id AND
c1.email = c2.email;
B) Delete duplicate rows using an intermediate table
The following shows the steps for removing duplicate rows using an intermediate table:
1. Create a new table with the structure the same as the original table that you want to delete duplicate rows.
2. Insert distinct rows from the original table to the immediate table.
3. Insert distinct rows from the original table to the immediate table.
Step 1. Create a new table whose structure is the same as the original table:
CREATE TABLE source_copy LIKE source;
Step 2. Insert distinct rows from the original table to the new table:
INSERT INTO source_copy
SELECT * FROM source
GROUP BY col; -- column that has duplicate values
Step 3. drop the original table and rename the immediate table to the original one
DROP TABLE source;
ALTER TABLE source_copy RENAME TO source;
Source: http://www.mysqltutorial.org/mysql-delete-duplicate-rows/
Please see the below way of deletion too.
Declare #table table
(col1 varchar(10),col2 int,col3 int, col4 int, col5 int, col6 int, col7 int)
Insert into #table values
('john',1,1,1,1,1,1),
('john',1,1,1,1,1,1),
('sally',2,2,2,2,2,2),
('sally',2,2,2,2,2,2)
Created a sample table named #table and loaded it with given data.
Delete aliasName from (
Select *,
ROW_NUMBER() over (Partition by col1,col2,col3,col4,col5,col6,col7 order by col1) as rowNumber
From #table) aliasName
Where rowNumber > 1
Select * from #table
Note: If you are giving all columns in the Partition by part, then order by do not have much significance.
I know, the question is asked three years ago, and my answer is another version of what Tim has posted, But posting just incase it is helpful for anyone.
It can be done by many ways in sql server
the most simplest way to do so is:
Insert the distinct rows from the duplicate rows table to new temporary table. Then delete all the data from duplicate rows table then insert all data from temporary table which has no duplicates as shown below.
select distinct * into #tmp From table
delete from table
insert into table
select * from #tmp drop table #tmp
select * from table
Delete duplicate rows using Common Table Expression(CTE)
With CTE_Duplicates as
(select id,name , row_number()
over(partition by id,name order by id,name ) rownumber from table )
delete from CTE_Duplicates where rownumber!=1
To delete the duplicate rows from the table in SQL Server, you follow these steps:
Find duplicate rows using GROUP BY clause or ROW_NUMBER() function.
Use DELETE statement to remove the duplicate rows.
Setting up a sample table
DROP TABLE IF EXISTS contacts;
CREATE TABLE contacts(
contact_id INT IDENTITY(1,1) PRIMARY KEY,
first_name NVARCHAR(100) NOT NULL,
last_name NVARCHAR(100) NOT NULL,
email NVARCHAR(255) NOT NULL,
);
Insert values
INSERT INTO contacts
(first_name,last_name,email)
VALUES
('Syed','Abbas','syed.abbas#example.com'),
('Catherine','Abel','catherine.abel#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Hazem','Abolrous','hazem.abolrous#example.com'),
('Hazem','Abolrous','hazem.abolrous#example.com'),
('Humberto','Acevedo','humberto.acevedo#example.com'),
('Humberto','Acevedo','humberto.acevedo#example.com'),
('Pilar','Ackerman','pilar.ackerman#example.com');
Query
SELECT
contact_id,
first_name,
last_name,
email
FROM
contacts;
Delete duplicate rows from a table
WITH cte AS (
SELECT
contact_id,
first_name,
last_name,
email,
ROW_NUMBER() OVER (
PARTITION BY
first_name,
last_name,
email
ORDER BY
first_name,
last_name,
email
) row_num
FROM
contacts
)
DELETE FROM cte
WHERE row_num > 1;
Should delete the record now
Try to Use:
SELECT linkorder
,Row_Number() OVER (
PARTITION BY linkorder ORDER BY linkorder DESC
) AS RowNum
FROM u_links
Microsoft has a vey ry neat guide on how to remove duplicates. Check out http://support.microsoft.com/kb/139444
In brief, here is the easiest way to delete duplicates when you have just a few rows to delete:
SET rowcount 1;
DELETE FROM t1 WHERE myprimarykey=1;
myprimarykey is the identifier for the row.
I set rowcount to 1 because I only had two rows that were duplicated. If I had had 3 rows duplicated then I would have set rowcount to 2 so that it deletes the first two that it sees and only leaves one in table t1.
with myCTE
as
(
select productName,ROW_NUMBER() over(PARTITION BY productName order by slno) as Duplicate from productDetails
)
Delete from myCTE where Duplicate>1
After trying the suggested solution above, that works for small medium tables.
I can suggest that solution for very large tables. since it runs in iterations.
Drop all dependency views of the LargeSourceTable
you can find the dependecies by using sql managment studio, right click on the table and click "View Dependencies"
Rename the table:
sp_rename 'LargeSourceTable', 'LargeSourceTable_Temp'; GO
Create the LargeSourceTable again, but now, add a primary key with all the columns that define the duplications add WITH (IGNORE_DUP_KEY = ON)
For example:
CREATE TABLE [dbo].[LargeSourceTable]
(
ID int IDENTITY(1,1),
[CreateDate] DATETIME CONSTRAINT [DF_LargeSourceTable_CreateDate] DEFAULT (getdate()) NOT NULL,
[Column1] CHAR (36) NOT NULL,
[Column2] NVARCHAR (100) NOT NULL,
[Column3] CHAR (36) NOT NULL,
PRIMARY KEY (Column1, Column2) WITH (IGNORE_DUP_KEY = ON)
);
GO
Create again the views that you dropped in the first place for the new created table
Now, Run the following sql script, you will see the results in 1,000,000 rows per page, you can change the row number per page to see the results more often.
Note, that I set the IDENTITY_INSERT on and off because one the columns contains auto incremental id, which I'm also copying
SET IDENTITY_INSERT LargeSourceTable ON
DECLARE #PageNumber AS INT, #RowspPage AS INT
DECLARE #TotalRows AS INT
declare #dt varchar(19)
SET #PageNumber = 0
SET #RowspPage = 1000000
select #TotalRows = count (*) from LargeSourceTable_TEMP
While ((#PageNumber - 1) * #RowspPage < #TotalRows )
Begin
begin transaction tran_inner
; with cte as
(
SELECT * FROM LargeSourceTable_TEMP ORDER BY ID
OFFSET ((#PageNumber) * #RowspPage) ROWS
FETCH NEXT #RowspPage ROWS ONLY
)
INSERT INTO LargeSourceTable
(
ID
,[CreateDate]
,[Column1]
,[Column2]
,[Column3]
)
select
ID
,[CreateDate]
,[Column1]
,[Column2]
,[Column3]
from cte
commit transaction tran_inner
PRINT 'Page: ' + convert(varchar(10), #PageNumber)
PRINT 'Transfered: ' + convert(varchar(20), #PageNumber * #RowspPage)
PRINT 'Of: ' + convert(varchar(20), #TotalRows)
SELECT #dt = convert(varchar(19), getdate(), 121)
RAISERROR('Inserted on: %s', 0, 1, #dt) WITH NOWAIT
SET #PageNumber = #PageNumber + 1
End
SET IDENTITY_INSERT LargeSourceTable OFF
-- this query will keep only one instance of a duplicate record.
;WITH cte
AS (SELECT ROW_NUMBER() OVER (PARTITION BY col1, col2, col3-- based on what? --can be multiple columns
ORDER BY ( SELECT 0)) RN
FROM Mytable)
delete FROM cte
WHERE RN > 1
You need to group by the duplicate records according to the field(s), then hold one of the records and delete the rest.
For example:
DELETE prg.Person WHERE Id IN (
SELECT dublicateRow.Id FROM
(
select MIN(Id) MinId, NationalCode
from prg.Person group by NationalCode having count(NationalCode ) > 1
) GroupSelect
JOIN prg.Person dublicateRow ON dublicateRow.NationalCode = GroupSelect.NationalCode
WHERE dublicateRow.Id <> GroupSelect.MinId)
Deleting duplicates from a huge(several millions of records) table might take long time . I suggest that you do a bulk insert into a temp table of the selected rows rather than deleting.
--REWRITING YOUR CODE(TAKE NOTE OF THE 3RD LINE) WITH CTE AS(SELECT NAME,ROW_NUMBER()
OVER (PARTITION BY NAME ORDER BY NAME) ID FROM #TB) SELECT * INTO #unique_records FROM
CTE WHERE ID =1;
This might help in your case
DELETE t1 FROM table t1 INNER JOIN table t2 WHERE t1.id > t2.id AND t1.col1 = t2.col1
With reference to https://support.microsoft.com/en-us/help/139444/how-to-remove-duplicate-rows-from-a-table-in-sql-server
The idea of removing duplicate involves
a) Protecting those rows that are not duplicate
b) Retain one of the many rows that qualified together as duplicate.
Step-by-step
1) First identify the rows those satisfy the definition of duplicate
and insert them into temp table, say #tableAll .
2) Select non-duplicate(single-rows) or distinct rows into temp table
say #tableUnique.
3) Delete from source table joining #tableAll to delete the
duplicates.
4) Insert into source table all the rows from #tableUnique.
5) Drop #tableAll and #tableUnique
If you have the ability to add a column to the table temporarily, this was a solution that worked for me:
ALTER TABLE dbo.DUPPEDTABLE ADD RowID INT NOT NULL IDENTITY(1,1)
Then perform a DELETE using a combination of MIN and GROUP BY
DELETE b
FROM dbo.DUPPEDTABLE b
WHERE b.RowID NOT IN (
SELECT MIN(RowID) AS RowID
FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
GROUP BY a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE
);
Verify that the DELETE performed correctly:
SELECT a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE, COUNT(*)--MIN(RowID) AS RowID
FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
GROUP BY a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE
ORDER BY COUNT(*) DESC
The result should have no rows with a count greater than 1. Finally, remove the rowid column:
ALTER TABLE dbo.DUPPEDTABLE DROP COLUMN RowID;
Oh wow, i feel so stupid by ready all this answers, they are like experts' answer with all CTE and temp table and etc.
And all I did to get it working was simply aggregated the ID column by using MAX.
DELETE FROM table WHERE col1 IN (
SELECT MAX(id) FROM table GROUP BY id HAVING ( COUNT(col1) > 1 )
)
NOTE: you might need to run it multiple time to remove duplicate as this will only delete one set of duplicate rows at a time.
please simply add the keyword DISTINCT right after the SELECT command,
for example:
SELECT DISTICNT ColumnOne, ColumnTwo, ColumnThree
FROM YourTable
Another way of removing dublicated rows without loosing information in one step is like following:
delete from dublicated_table t1 (nolock)
join (
select t2.dublicated_field
, min(len(t2.field_kept)) as min_field_kept
from dublicated_table t2 (nolock)
group by t2.dublicated_field having COUNT(*)>1
) t3
on t1.dublicated_field=t3.dublicated_field
and len(t1.field_kept)=t3.min_field_kept
DECLARE #TB TABLE(NAME VARCHAR(100));
INSERT INTO #TB VALUES ('Red'),('Red'),('Green'),('Blue'),('White'),('White')
--**Delete by Rank**
;WITH CTE AS(SELECT NAME,DENSE_RANK() OVER (PARTITION BY NAME ORDER BY NEWID()) ID FROM #TB)
DELETE FROM CTE WHERE ID>1
SELECT NAME FROM #TB;
--**Delete by Row Number**
;WITH CTE AS(SELECT NAME,ROW_NUMBER() OVER (PARTITION BY NAME ORDER BY NAME) ID FROM #TB)
DELETE FROM CTE WHERE ID>1;
SELECT NAME FROM #TB;
DELETE FROM TBL1 WHERE ID IN
(SELECT ID FROM TBL1 a WHERE ID!=
(select MAX(ID) from TBL1 where DUPVAL=a.DUPVAL
group by DUPVAL
having count(DUPVAL)>1))
DELETE p1 FROM Person p1,
Person p2
WHERE
p1.Email = p2.Email AND p1.Id > p2.Id
I have a query having cte with number of columns, I want to insert a record if ID from the results of that query does not exist in table that I am inserting, or if the ID exists I want to update data using that ID.
So far I have tried this:
WITH cte_base as(
SELECT DISTINCT ID, statusID
FROM testtable
)
SELECT *
FROM cte_base
IF EXISTS(SELECT * FROM Newtable WHERE EXISTS (SELECT ID FROM cte_base))
UPDATE newtable
SET statusID = 2
WHERE Newtable.ID = cte_base.ID
ELSE
INSERT INTO newtable(ID, statusID)
SELECT ID, statusID
FROM cte_base
WHERE Newtable.ID <> cte_base.ID
I have to run this query against live data, hence I would like to know if my logic is correct.
Basic merge example based on your provided code.
MERGE INTO NewTable AS T
USING
(
SELECT DISTINCT ID,statusID
FROM testtable
) AS S
ON S.ID = T.ID
WHEN MATCHED THEN SET
T.StatusID = 2
WHEN NOT MATCHED INSERT (ID,statusID)
VALUES (S.ID,S.statusID)
;
What are you trying to do?
EXISTS (SELECT ID FROM cte_base)
If cte_base has any records that will be true every time
That is no different than
SELECT DISTINCT ID, statusID
FROM testtable
And will be true every time if there are any records in testtable
I am trying to delete some duplicate data in my redshift table.
Below is my query:-
With duplicates
As
(Select *, ROW_NUMBER() Over (PARTITION by record_indicator Order by record_indicator) as Duplicate From table_name)
delete from duplicates
Where Duplicate > 1 ;
This query is giving me an error.
Amazon Invalid operation: syntax error at or near "delete";
Not sure what the issue is as the syntax for with clause seems to be correct.
Has anybody faced this situation before?
Redshift being what it is (no enforced uniqueness for any column), Ziggy's 3rd option is probably best. Once we decide to go the temp table route it is more efficient to swap things out whole. Deletes and inserts are expensive in Redshift.
begin;
create table table_name_new as select distinct * from table_name;
alter table table_name rename to table_name_old;
alter table table_name_new rename to table_name;
drop table table_name_old;
commit;
If space isn't an issue you can keep the old table around for a while and use the other methods described here to validate that the row count in the original accounting for duplicates matches the row count in the new.
If you're doing constant loads to such a table you'll want to pause that process while this is going on.
If the number of duplicates is a small percentage of a large table, you might want to try copying distinct records of the duplicates to a temp table, then delete all records from the original that join with the temp. Then append the temp table back to the original. Make sure you vacuum the original table after (which you should be doing for large tables on a schedule anyway).
If you're dealing with a lot of data it's not always possible or smart to recreate the whole table. It may be easier to locate, delete those rows:
-- First identify all the rows that are duplicate
CREATE TEMP TABLE duplicate_saleids AS
SELECT saleid
FROM sales
WHERE saledateid BETWEEN 2224 AND 2231
GROUP BY saleid
HAVING COUNT(*) > 1;
-- Extract one copy of all the duplicate rows
CREATE TEMP TABLE new_sales(LIKE sales);
INSERT INTO new_sales
SELECT DISTINCT *
FROM sales
WHERE saledateid BETWEEN 2224 AND 2231
AND saleid IN(
SELECT saleid
FROM duplicate_saleids
);
-- Remove all rows that were duplicated (all copies).
DELETE FROM sales
WHERE saledateid BETWEEN 2224 AND 2231
AND saleid IN(
SELECT saleid
FROM duplicate_saleids
);
-- Insert back in the single copies
INSERT INTO sales
SELECT *
FROM new_sales;
-- Cleanup
DROP TABLE duplicate_saleids;
DROP TABLE new_sales;
COMMIT;
Full article: https://elliot.land/post/removing-duplicate-data-in-redshift
That should have worked. Alternative you can do:
With
duplicates As (
Select *, ROW_NUMBER() Over (PARTITION by record_indicator
Order by record_indicator) as Duplicate
From table_name)
delete from table_name
where id in (select id from duplicates Where Duplicate > 1);
or
delete from table_name
where id in (
select id
from (
Select id, ROW_NUMBER() Over (PARTITION by record_indicator
Order by record_indicator) as Duplicate
From table_name) x
Where Duplicate > 1);
If you have no primary key, you can do the following:
BEGIN;
CREATE TEMP TABLE mydups ON COMMIT DROP AS
SELECT DISTINCT ON (record_indicator) *
FROM table_name
ORDER BY record_indicator --, other_optional_priority_field DESC
;
DELETE FROM table_name
WHERE record_indicator IN (
SELECT record_indicator FROM mydups);
INSERT INTO table_name SELECT * FROM mydups;
COMMIT;
This method will preserve permissions and the table definition of the original_table.
The most upvoted answer does not preserve permissions on the table or the original definition of the table.
In real world production environment this method is how you should be doing as this is safest and easiest way to execute in production environment.
This will have a DOWN TIME in PROD.
Create Table with unique rows
CREATE TABLE unique_table as
(
SELECT DISTINCT * FROM original_table
)
;
Backup the original_table
CREATE TABLE backup_table as
(
SELECT * FROM original_table
)
;
Truncate the original_table
TRUNCATE original_table;
Insert records from unique_table into original_table
INSERT INTO original_table
(
SELECT * FROM unique_table
)
;
To avoid DOWN TIME run the below queries in a TRANSACTION and instead of TRUNCATE use DELETE
BEGIN transaction;
CREATE TABLE unique_table as
(
SELECT DISTINCT * FROM original_table
)
;
CREATE TABLE backup_table as
(
SELECT * FROM original_table
)
;
DELETE FROM original_table;
INSERT INTO original_table
(
SELECT * FROM unique_table
)
;
END transaction;
Simple answer to this question:
Firstly create a temporary table from the main table where value of row_number=1.
Secondly delete all the rows from the main table on which we had duplicates.
Then insert the values of temporary table into the main table.
Queries:
Temporary table
select id,date into #temp_a
from
(select *
from (select a.*,
row_number() over(partition by id order by etl_createdon desc) as rn
from table a
where a.id between 59 and 75 and a.date = '2018-05-24')
where rn =1)a
deleting all the rows from the main table.
delete from table a
where a.id between 59 and 75 and a.date = '2018-05-24'
inserting all values from temp table to main table
insert into table a select * from #temp_a.
The following deletes all records in 'tablename' that have a duplicate, it will not deduplicate the table:
DELETE FROM tablename
WHERE id IN (
SELECT id
FROM (
SELECT id,
ROW_NUMBER() OVER (partition BY column1, column2, column3 ORDER BY id) AS rnum
FROM tablename
) t
WHERE t.rnum > 1);
Postgres administrative snippets
Your query does not work because Redshift does not allow DELETE after the WITH clause. Only SELECT and UPDATE and a few others are allowed (see WITH clause)
Solution (in my situation):
I did have an id column on my table events that contained duplicate rows and uniquely identifies the record. This column id is the same as your record_indicator.
Unfortunately I was unable to create a temporary table because I ran into the following error using SELECT DISTINCT:
ERROR: Intermediate result row exceeds database block size
But this worked like a charm:
CREATE TABLE temp as (
SELECT *,ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS rownumber
FROM events
);
resulting in the temp table:
id | rownumber | ...
----------------
1 | 1 | ...
1 | 2 | ...
2 | 1 | ...
2 | 2 | ...
Now the duplicates can be deleted by removing the rows having rownumber larger than 1:
DELETE FROM temp WHERE rownumber > 1
After that rename the tables and your done.
with duplicates as
(
select a.*, row_number (over (partition by first_name, last_name, email order by first_name, last_name, email) as rn from contacts a
)
delete from contacts
where contact_id in (
select contact_id from duplicates where rn >1
)
How can I delete duplicate rows where no unique row id exists?
My table is
col1 col2 col3 col4 col5 col6 col7
john 1 1 1 1 1 1
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
sally 2 2 2 2 2 2
I want to be left with the following after the duplicate removal:
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
I've tried a few queries but I think they depend on having a row id as I don't get the desired result. For example:
DELETE
FROM table
WHERE col1 IN (
SELECT id
FROM table
GROUP BY id
HAVING (COUNT(col1) > 1)
)
I like CTEs and ROW_NUMBER as the two combined allow us to see which rows are deleted (or updated), therefore just change the DELETE FROM CTE... to SELECT * FROM CTE:
WITH CTE AS(
SELECT [col1], [col2], [col3], [col4], [col5], [col6], [col7],
RN = ROW_NUMBER()OVER(PARTITION BY col1 ORDER BY col1)
FROM dbo.Table1
)
DELETE FROM CTE WHERE RN > 1
DEMO (result is different; I assume that it's due to a typo on your part)
COL1 COL2 COL3 COL4 COL5 COL6 COL7
john 1 1 1 1 1 1
sally 2 2 2 2 2 2
This example determines duplicates by a single column col1 because of the PARTITION BY col1. If you want to include multiple columns simply add them to the PARTITION BY:
ROW_NUMBER()OVER(PARTITION BY Col1, Col2, ... ORDER BY OrderColumn)
I would prefer CTE for deleting duplicate rows from sql server table
strongly recommend to follow this article ::http://codaffection.com/sql-server-article/delete-duplicate-rows-in-sql-server/
by keeping original
WITH CTE AS
(
SELECT *,ROW_NUMBER() OVER (PARTITION BY col1,col2,col3 ORDER BY col1,col2,col3) AS RN
FROM MyTable
)
DELETE FROM CTE WHERE RN<>1
without keeping original
WITH CTE AS
(SELECT *,R=RANK() OVER (ORDER BY col1,col2,col3)
FROM MyTable)
DELETE CTE
WHERE R IN (SELECT R FROM CTE GROUP BY R HAVING COUNT(*)>1)
Without using CTE and ROW_NUMBER() you can just delete the records just by using group by with MAX function here is an example
DELETE
FROM MyDuplicateTable
WHERE ID NOT IN
(
SELECT MAX(ID)
FROM MyDuplicateTable
GROUP BY DuplicateColumn1, DuplicateColumn2, DuplicateColumn3)
If you have no references, like foreign keys, you can do this. I do it a lot when testing proofs of concept and the test data gets duplicated.
SELECT DISTINCT [col1],[col2],[col3],[col4],[col5],[col6],[col7]
INTO [newTable]
FROM [oldTable]
Go into the object explorer and delete the old table.
Rename the new table with the old table's name.
Remove all duplicates, but the very first ones (with min ID)
should work equally in other SQL servers, like Postgres:
DELETE FROM table
WHERE id NOT IN (
select min(id) from table
group by col1, col2, col3, col4, col5, col6, col7
)
DELETE from search
where id not in (
select min(id) from search
group by url
having count(*)=1
union
SELECT min(id) FROM search
group by url
having count(*) > 1
)
There are two solutions in mysql:
A) Delete duplicate rows using DELETE JOIN statement
DELETE t1 FROM contacts t1
INNER JOIN contacts t2
WHERE
t1.id < t2.id AND
t1.email = t2.email;
This query references the contacts table twice, therefore, it uses the table alias t1 and t2.
The output is:
1
Query OK, 4 rows affected (0.10 sec)
In case you want to delete duplicate rows and keep the lowest id, you can use the following statement:
DELETE c1 FROM contacts c1
INNER JOIN contacts c2
WHERE
c1.id > c2.id AND
c1.email = c2.email;
B) Delete duplicate rows using an intermediate table
The following shows the steps for removing duplicate rows using an intermediate table:
1. Create a new table with the structure the same as the original table that you want to delete duplicate rows.
2. Insert distinct rows from the original table to the immediate table.
3. Insert distinct rows from the original table to the immediate table.
Step 1. Create a new table whose structure is the same as the original table:
CREATE TABLE source_copy LIKE source;
Step 2. Insert distinct rows from the original table to the new table:
INSERT INTO source_copy
SELECT * FROM source
GROUP BY col; -- column that has duplicate values
Step 3. drop the original table and rename the immediate table to the original one
DROP TABLE source;
ALTER TABLE source_copy RENAME TO source;
Source: http://www.mysqltutorial.org/mysql-delete-duplicate-rows/
Please see the below way of deletion too.
Declare #table table
(col1 varchar(10),col2 int,col3 int, col4 int, col5 int, col6 int, col7 int)
Insert into #table values
('john',1,1,1,1,1,1),
('john',1,1,1,1,1,1),
('sally',2,2,2,2,2,2),
('sally',2,2,2,2,2,2)
Created a sample table named #table and loaded it with given data.
Delete aliasName from (
Select *,
ROW_NUMBER() over (Partition by col1,col2,col3,col4,col5,col6,col7 order by col1) as rowNumber
From #table) aliasName
Where rowNumber > 1
Select * from #table
Note: If you are giving all columns in the Partition by part, then order by do not have much significance.
I know, the question is asked three years ago, and my answer is another version of what Tim has posted, But posting just incase it is helpful for anyone.
It can be done by many ways in sql server
the most simplest way to do so is:
Insert the distinct rows from the duplicate rows table to new temporary table. Then delete all the data from duplicate rows table then insert all data from temporary table which has no duplicates as shown below.
select distinct * into #tmp From table
delete from table
insert into table
select * from #tmp drop table #tmp
select * from table
Delete duplicate rows using Common Table Expression(CTE)
With CTE_Duplicates as
(select id,name , row_number()
over(partition by id,name order by id,name ) rownumber from table )
delete from CTE_Duplicates where rownumber!=1
To delete the duplicate rows from the table in SQL Server, you follow these steps:
Find duplicate rows using GROUP BY clause or ROW_NUMBER() function.
Use DELETE statement to remove the duplicate rows.
Setting up a sample table
DROP TABLE IF EXISTS contacts;
CREATE TABLE contacts(
contact_id INT IDENTITY(1,1) PRIMARY KEY,
first_name NVARCHAR(100) NOT NULL,
last_name NVARCHAR(100) NOT NULL,
email NVARCHAR(255) NOT NULL,
);
Insert values
INSERT INTO contacts
(first_name,last_name,email)
VALUES
('Syed','Abbas','syed.abbas#example.com'),
('Catherine','Abel','catherine.abel#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Kim','Abercrombie','kim.abercrombie#example.com'),
('Hazem','Abolrous','hazem.abolrous#example.com'),
('Hazem','Abolrous','hazem.abolrous#example.com'),
('Humberto','Acevedo','humberto.acevedo#example.com'),
('Humberto','Acevedo','humberto.acevedo#example.com'),
('Pilar','Ackerman','pilar.ackerman#example.com');
Query
SELECT
contact_id,
first_name,
last_name,
email
FROM
contacts;
Delete duplicate rows from a table
WITH cte AS (
SELECT
contact_id,
first_name,
last_name,
email,
ROW_NUMBER() OVER (
PARTITION BY
first_name,
last_name,
email
ORDER BY
first_name,
last_name,
email
) row_num
FROM
contacts
)
DELETE FROM cte
WHERE row_num > 1;
Should delete the record now
Try to Use:
SELECT linkorder
,Row_Number() OVER (
PARTITION BY linkorder ORDER BY linkorder DESC
) AS RowNum
FROM u_links
Microsoft has a vey ry neat guide on how to remove duplicates. Check out http://support.microsoft.com/kb/139444
In brief, here is the easiest way to delete duplicates when you have just a few rows to delete:
SET rowcount 1;
DELETE FROM t1 WHERE myprimarykey=1;
myprimarykey is the identifier for the row.
I set rowcount to 1 because I only had two rows that were duplicated. If I had had 3 rows duplicated then I would have set rowcount to 2 so that it deletes the first two that it sees and only leaves one in table t1.
with myCTE
as
(
select productName,ROW_NUMBER() over(PARTITION BY productName order by slno) as Duplicate from productDetails
)
Delete from myCTE where Duplicate>1
After trying the suggested solution above, that works for small medium tables.
I can suggest that solution for very large tables. since it runs in iterations.
Drop all dependency views of the LargeSourceTable
you can find the dependecies by using sql managment studio, right click on the table and click "View Dependencies"
Rename the table:
sp_rename 'LargeSourceTable', 'LargeSourceTable_Temp'; GO
Create the LargeSourceTable again, but now, add a primary key with all the columns that define the duplications add WITH (IGNORE_DUP_KEY = ON)
For example:
CREATE TABLE [dbo].[LargeSourceTable]
(
ID int IDENTITY(1,1),
[CreateDate] DATETIME CONSTRAINT [DF_LargeSourceTable_CreateDate] DEFAULT (getdate()) NOT NULL,
[Column1] CHAR (36) NOT NULL,
[Column2] NVARCHAR (100) NOT NULL,
[Column3] CHAR (36) NOT NULL,
PRIMARY KEY (Column1, Column2) WITH (IGNORE_DUP_KEY = ON)
);
GO
Create again the views that you dropped in the first place for the new created table
Now, Run the following sql script, you will see the results in 1,000,000 rows per page, you can change the row number per page to see the results more often.
Note, that I set the IDENTITY_INSERT on and off because one the columns contains auto incremental id, which I'm also copying
SET IDENTITY_INSERT LargeSourceTable ON
DECLARE #PageNumber AS INT, #RowspPage AS INT
DECLARE #TotalRows AS INT
declare #dt varchar(19)
SET #PageNumber = 0
SET #RowspPage = 1000000
select #TotalRows = count (*) from LargeSourceTable_TEMP
While ((#PageNumber - 1) * #RowspPage < #TotalRows )
Begin
begin transaction tran_inner
; with cte as
(
SELECT * FROM LargeSourceTable_TEMP ORDER BY ID
OFFSET ((#PageNumber) * #RowspPage) ROWS
FETCH NEXT #RowspPage ROWS ONLY
)
INSERT INTO LargeSourceTable
(
ID
,[CreateDate]
,[Column1]
,[Column2]
,[Column3]
)
select
ID
,[CreateDate]
,[Column1]
,[Column2]
,[Column3]
from cte
commit transaction tran_inner
PRINT 'Page: ' + convert(varchar(10), #PageNumber)
PRINT 'Transfered: ' + convert(varchar(20), #PageNumber * #RowspPage)
PRINT 'Of: ' + convert(varchar(20), #TotalRows)
SELECT #dt = convert(varchar(19), getdate(), 121)
RAISERROR('Inserted on: %s', 0, 1, #dt) WITH NOWAIT
SET #PageNumber = #PageNumber + 1
End
SET IDENTITY_INSERT LargeSourceTable OFF
-- this query will keep only one instance of a duplicate record.
;WITH cte
AS (SELECT ROW_NUMBER() OVER (PARTITION BY col1, col2, col3-- based on what? --can be multiple columns
ORDER BY ( SELECT 0)) RN
FROM Mytable)
delete FROM cte
WHERE RN > 1
You need to group by the duplicate records according to the field(s), then hold one of the records and delete the rest.
For example:
DELETE prg.Person WHERE Id IN (
SELECT dublicateRow.Id FROM
(
select MIN(Id) MinId, NationalCode
from prg.Person group by NationalCode having count(NationalCode ) > 1
) GroupSelect
JOIN prg.Person dublicateRow ON dublicateRow.NationalCode = GroupSelect.NationalCode
WHERE dublicateRow.Id <> GroupSelect.MinId)
Deleting duplicates from a huge(several millions of records) table might take long time . I suggest that you do a bulk insert into a temp table of the selected rows rather than deleting.
--REWRITING YOUR CODE(TAKE NOTE OF THE 3RD LINE) WITH CTE AS(SELECT NAME,ROW_NUMBER()
OVER (PARTITION BY NAME ORDER BY NAME) ID FROM #TB) SELECT * INTO #unique_records FROM
CTE WHERE ID =1;
This might help in your case
DELETE t1 FROM table t1 INNER JOIN table t2 WHERE t1.id > t2.id AND t1.col1 = t2.col1
With reference to https://support.microsoft.com/en-us/help/139444/how-to-remove-duplicate-rows-from-a-table-in-sql-server
The idea of removing duplicate involves
a) Protecting those rows that are not duplicate
b) Retain one of the many rows that qualified together as duplicate.
Step-by-step
1) First identify the rows those satisfy the definition of duplicate
and insert them into temp table, say #tableAll .
2) Select non-duplicate(single-rows) or distinct rows into temp table
say #tableUnique.
3) Delete from source table joining #tableAll to delete the
duplicates.
4) Insert into source table all the rows from #tableUnique.
5) Drop #tableAll and #tableUnique
If you have the ability to add a column to the table temporarily, this was a solution that worked for me:
ALTER TABLE dbo.DUPPEDTABLE ADD RowID INT NOT NULL IDENTITY(1,1)
Then perform a DELETE using a combination of MIN and GROUP BY
DELETE b
FROM dbo.DUPPEDTABLE b
WHERE b.RowID NOT IN (
SELECT MIN(RowID) AS RowID
FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
GROUP BY a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE
);
Verify that the DELETE performed correctly:
SELECT a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE, COUNT(*)--MIN(RowID) AS RowID
FROM dbo.DUPPEDTABLE a WITH (NOLOCK)
GROUP BY a.ITEM_NUMBER,
a.CHARACTERISTIC,
a.INTVALUE,
a.FLOATVALUE,
a.STRINGVALUE
ORDER BY COUNT(*) DESC
The result should have no rows with a count greater than 1. Finally, remove the rowid column:
ALTER TABLE dbo.DUPPEDTABLE DROP COLUMN RowID;
Oh wow, i feel so stupid by ready all this answers, they are like experts' answer with all CTE and temp table and etc.
And all I did to get it working was simply aggregated the ID column by using MAX.
DELETE FROM table WHERE col1 IN (
SELECT MAX(id) FROM table GROUP BY id HAVING ( COUNT(col1) > 1 )
)
NOTE: you might need to run it multiple time to remove duplicate as this will only delete one set of duplicate rows at a time.
please simply add the keyword DISTINCT right after the SELECT command,
for example:
SELECT DISTICNT ColumnOne, ColumnTwo, ColumnThree
FROM YourTable
Another way of removing dublicated rows without loosing information in one step is like following:
delete from dublicated_table t1 (nolock)
join (
select t2.dublicated_field
, min(len(t2.field_kept)) as min_field_kept
from dublicated_table t2 (nolock)
group by t2.dublicated_field having COUNT(*)>1
) t3
on t1.dublicated_field=t3.dublicated_field
and len(t1.field_kept)=t3.min_field_kept
DECLARE #TB TABLE(NAME VARCHAR(100));
INSERT INTO #TB VALUES ('Red'),('Red'),('Green'),('Blue'),('White'),('White')
--**Delete by Rank**
;WITH CTE AS(SELECT NAME,DENSE_RANK() OVER (PARTITION BY NAME ORDER BY NEWID()) ID FROM #TB)
DELETE FROM CTE WHERE ID>1
SELECT NAME FROM #TB;
--**Delete by Row Number**
;WITH CTE AS(SELECT NAME,ROW_NUMBER() OVER (PARTITION BY NAME ORDER BY NAME) ID FROM #TB)
DELETE FROM CTE WHERE ID>1;
SELECT NAME FROM #TB;
DELETE FROM TBL1 WHERE ID IN
(SELECT ID FROM TBL1 a WHERE ID!=
(select MAX(ID) from TBL1 where DUPVAL=a.DUPVAL
group by DUPVAL
having count(DUPVAL)>1))
DELETE p1 FROM Person p1,
Person p2
WHERE
p1.Email = p2.Email AND p1.Id > p2.Id