Remove duplicate rows in MySQL

Question

I have a table with the following fields:

id (Unique)
url (Unique)
title
company
site_id

Now, I need to remove rows having same titl

Answer 1

A solution that is simple to understand and works with no primary key:

1) add a new boolean column

alter table mytable add tokeep boolean;

2) add a constraint on the duplicated columns AND the new column

alter table mytable add constraint preventdupe unique (mycol1, mycol2, tokeep);

3) set the boolean column to true. This will succeed only on one of the duplicated rows because of the new constraint

update ignore mytable set tokeep = true;

4) delete rows that have not been marked as tokeep

delete from mytable where tokeep is null;

5) drop the added column

alter table mytable drop tokeep;

I suggest that you keep the constraint you added, so that new duplicates are prevented in the future.