Delete duplicate rows (don't delete all duplicate)

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I am using postgres. I want to delete Duplicate rows. The condition is that , 1 copy from the set of duplicate rows would not be deleted.

i.e : if there are 5 duplicate records then 4 of them will be deleted.

Try the steps described in this article: Removing duplicates from a PostgreSQL database.

It describes a situation when you have to deal with huge amount of data which isn't possible to group by.

A simple solution would be this:

DELETE FROM foo
       WHERE id NOT IN (SELECT min(id) --or max(id)
                        FROM foo
                        GROUP BY hash)

Where hash is something that gets duplicated.

How to delete duplicate rows in SQL Server?, 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� To remove duplicate rows using the Advanced Filter: Select the data that you want to remove the duplicates from (columns A-C in the example spreadsheet Select the Excel Advanced Filter option from the Data tab at the top of your Excel workbook (or in Excel 2003, this You will be presented with

delete from table
where not id in 
(select max(id) from table group by [duplicate row])

This is random (max Value) choice which row you need to keep. If you have aggre whit this please provide more details

How to Remove Duplicate Rows in Excel, Getting Started. Today we will talk about a few handy methods for identifying and deleting duplicate rows in Excel. If you don't have any files with� Select the range you want to remove duplicate rows. If you want to delete all duplicate rows in the worksheet, just hold down Ctrl + A key to select the entire sheet. 2. On Data tab, click Remove Duplicates in the Data Tools group. 3. In the Remove Duplicates dialog box, leave all the checkboxes checked under Columns list box, and if your data

The fastest is is join to the same table. http://www.postgresql.org/docs/8.1/interactive/sql-delete.html

CREATE TABLE test(id INT,id2 INT);
CREATE TABLE
mapy=# INSERT INTO test VALUES(1,2);
INSERT 0 1
mapy=# INSERT INTO test VALUES(1,3);
INSERT 0 1
mapy=# INSERT INTO test VALUES(1,4);
INSERT 0 1

DELETE FROM test t1 USING test t2 WHERE t1.id=t2.id AND t1.id2<t2.id2;
DELETE 2
mapy=# SELECT * FROM test;
 id | id2 
----+-----
  1 |   4
(1 row)

Delete duplicate rows with no primary key on a SQL Server table, So how do you delete the duplicate record? rather I'd have included them in a well identified section of the article to say "DON'T EVER DO THIS BECAUSE."� The following statement uses a common table expression (CTE) to delete duplicate rows: 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 sales.contacts) DELETE FROM cte WHERE row_num > 1 ;

delete from table t1 
where rowid > (SELECT min(rowid) FROM table t2 group by 
               t2.id,t2.name );

SQL query to delete duplicate rows, Delete duplicate rows using CTE. Understanding CTE query is bit difficult so if you still don't understand how CTE is working, no worries see Method3 same job � Remove duplicates but keep rest of row values with Filter With a formula and the Filter function, you can quickly remove duplicates but keep rest. 1. Select a blank cell next to the data range, D2 for instance, type formula =A3=A2, drag auto fill handle down to the cells you need.

Delete duplicate rows from Oracle tables, Oracle Database Tips by Donald Burleson. Removing duplicate rows from Oracle tables with SQL can be very tricky, and there are several techniques for� 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

Remove all rows/data from table at the start of Flow could be easily achieved using the following configuration. Please check the image for a reference. Note: If you have more than 256 rows, you need to set Top Count to its maximum value.

Determines which duplicates (if any) to keep. - first: Drop duplicates except for the first occurrence. - last: Drop duplicates except for the last occurrence. - False : Drop all duplicates. inplace bool, default False. Whether to drop duplicates in place or to return a copy. ignore_index bool, default False

Comments
  • possible duplicate of How to delete duplicate rows with SQL?
  • how ironic! lol 'possible duplicate of how to delete duplicates'...
  • doesn't this delete all the rows that don't have duplicates, too?
  • @pomarc no, because there's this little equals sign (=) before 1 that tells us that we want to take min(id) of all possible groups even those that contain only one member; so, no worries, you won't delete data that is not duplicated
  • is the having count (*) >=1 neccesary ? i got the same result if I execute : DELETE FROM foo WHERE id NOT IN (SELECT min(id) FROM foo GROUP BY hash)
  • @grteibo you are absolutely right, that's the way the deduplication is usually done; I don't know why I didn't notice that before; the idea of this answer is not so much the idea of deduplication itself but the fact that we calculate a hash for all the columns that we want to group by and then remove duplicates