Delete duplicated mysql rows with no primary key

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Hi i have a mysql table without primary key and i need to delete the duplicated rows. how can i do so?

user_id category_id
1            2
1            3
1            4
1            2
2            2
2            3
2            2
 CREATE TABLE temp SELECT DISTINCT * FROM tablename;
 ALTER TABLE tablename RENAME junk;
 ALTER TABLE temp RENAME tablename;

Delete duplicated mysql rows with no primary key, In this tutorial, you will learn how to delete duplicate rows in MySQL by using the DELETE MySQL delete duplicate rows - DELETE JOIN keeps Highest ID Was this tutorial helpful? YesNo. Previous How To Find Duplicate Values in MySQL. DELETE Duplicate Records Using ROWCOUNT. So to delete the duplicate record with SQL Server we can use the SET ROWCOUNT command to limit the number of rows affected by a query. By setting it to 1 we can just delete one of these rows in the table. Note: the select commands are just used to show the data prior and after the delete occurs.

Since you cannot differentiate 2 identical rows, you cannot delete just one of them. The way you need to think about it is like this:

insert into new_better_table
select user_id, category_id from old_table group by user_id, category_id

How To Delete Duplicate Rows in MySQL, ALTER TABLE products ADD COLUMN temp SERIAL PRIMARY KEY; DELETE t1.* FROM products t1 LEFT JOIN ( SELECT MIN(temp) mintemp FROM products​  To delete duplicate rows in our test MySQL table enter the following: delete t1 FROM dates t1 INNER JOIN dates t2 WHERE t1.id < t2.id AND t1.day = t2.day AND t1.month = t2.month AND t1.year = t2.year; You may also use the command from Display Duplicate Rows to verify the deletion.

It's possible to use a dirty flag with default value 1 and copy only single records with the flag set to 0, then simply remove all dirty records. This way you don't need another table.

Assuming you already created a dirty flag with default value 1:

insert into mytable
select fld1,fld2,fldN,0 as dirty
from mytable
group by duplicate_field

Then you can just delete dirty records:

delete from mytable where dirty = 1

Don't forget to remove the dirty flag. You're done.

How to delete duplicate records in MySQL, in a table without IDs , In the spirit of @yercube's answer, I have an answer that has an added twist. CREATE TABLE stage ( id int not null auto_increment, name  To remove duplicate you should have one unique key or primary key. Here my table name is 'table1' and id is unique key and col1 and col2 is my column name. You can remove all duplicate rows using this query :

remove duplicate rows in mysql table that does not contain primary key, To remove duplicate you should have one unique key or primary key. Here my table name is 'table1' and id is unique key and col1 and col2 is my column name. A) Delete duplicate rows using DELETE JOIN statement. MySQL provides you with the DELETE JOIN statement that allows you to remove duplicate rows quickly. The following statement deletes duplicate rows and keeps the highest id: DELETE t1 FROM contacts t1 INNER JOIN contacts t2 WHERE t1.id < t2.id AND t1.email = t2.email;

How to delete duplicate rows in MySQL without using adding new , Learn 3 ways how to remove duplicate rows from a MySQL table. CREATE TABLE dates ( id INT PRIMARY KEY AUTO_INCREMENT, day VARCHAR(2) NOT NULL, You can verify there are no duplicate rows by running: I am trying to delete duplicate rows except one duplicated record with the help of below query. DELETE FROM ( SELECT `name`,`rownumber` FROM (SELECT GREATEST(0,@num := IF(`name` = @NAME, @num + 1, 1),LEAST(1, LENGTH(@NAME := `name`))) AS rownumber,`name` FROM item ORDER BY `name`) AS result1 ) AS result WHERE rownumber >1

How to Remove Duplicate Rows in MySQL {3 Ways to Delete}, Deleting Rows with Non-unique Keys. In the case of JENNIFER DAVIS, who appears twice with the same id of 22, we would need to employ a  First solution: move unique records to a copy of table and replace original table. CREATE TABLE temp LIKE products; INSERT INTO temp SELECT DISTINCT * FROM products; DROP TABLE products; RENAME TABLE temp TO products; Second solution: add temporary autoincrement, delete records using it, and drop temp field.

Comments
  • duplicate user_id or duplicate category_id or complete row
  • Please show table definition. What is table's engine?
  • i think it must be DISTINCT(user_id)
  • @diEcho the OP asked for distinct rows - not distinct user_id.
  • @Damian :-) cool glad it works for you. Oh side note - you will lose any other indexes on your original table if you have them.
  • I agree with @adiran-cornish , you should copy the create statement of your table from a tool like workbench and use that create statement to retain the original table indexes
  • Saved me a lot of hassle bending my brain on how to do this by simulating row_number() and using group by, which I stopped trying to do now I know of :)
  • I think you could use a SELECT DISTINCT rather that a GROUP BY - not sure if there is an efficiency difference though.
  • Yeah. I generally prefer GROUP BY to DISTINCT because I find that it's more explicit and therefore clearer. I'm pretty sure performance will be identical on most (all?) systems. If there was ever a case to choose DISTINCT over GROUP BY... this is it. "DISTINCT *" is indeed much clearer than "GROUP BY [everything]". There's a big efficiency gain in the number of characters you need to type.
  • LOL :-) - am I right in thinking EXPLAIN wont work - be DBA pedant to know the answer which if any is better
  • I am terrible at ANSI SQL but I have a gut feeling DISTINCT is evaluated last - so GROUP BY might be more efficient - have to ask my friend who is a real DBA unlike me