Delete all but one duplicate record

Question

I have a table that is supposed to keep a trace of visitors to a given profile (user id to user id pair). It turns out my SQL query was a bit off and is producing multiple p

Answer 1

Here's Frank Schmitt's solution with a small workaround utilizing a temporary table to allow his solution to work on MySQL:

delete from `my_tab` where id not in
( SELECT * FROM 
    (select min(id) from `my_tab` group by profile_id, visitor_id) AS temp_tab
)

Answer 2

This will work:

With NewCTE
AS
(
Select *, Row_number() over(partition by ID order by ID)as RowNumber from 
table_name
)
Delete from NewCTE where RowNumber > 1

Answer 3

ANSI SQL Solution

Use group by in a subquery:

delete from my_tab where id not in 
(select min(id) from my_tab group by profile_id, visitor_id);

You need some kind of unique identifier(here, I'm using id).

MySQL Solution

As pointed out by @JamesPoulson, this causes a syntax error in MySQL; the correct solution is (as shown in James' answer):

delete from `my_tab` where id not in
( SELECT * FROM 
    (select min(id) from `my_tab` group by profile_id, visitor_id) AS temp_tab
);

Answer 4

Select all unique rows
Copy them to a new temp table
Truncate original table
Copy temp table data to original table

That's what I'd do. I'm not sure if there's 1 query that would do all this for you.

Answer 5

If you are using SQL you can manually delete the duplicate rows keeping one entry just follow this procedure:

1. Go into your table where you have duplicate data.
2. Apply the filter to segregate duplicate data for each individual id
3. Select all the rows you want to delete.
4. Press delete and save the result.
5. Repeat the process for each id you have duplicate entries for.

It's a long procedure but you can see the results immediately in real-time.

Hope this solution worked for you!!