Question: I am woking on PG `9.2.14` on our production server I am facing some random issue.

Let's say its a table named `users` and `id` is the primary key in it.

When I am trying to reindex the table it give me following error:-

```
ERROR:  could not create unique index "users_pkey"
DETAIL:  Key (id)=(339) is duplicated.

```

When I am trying to fetch user with the `339` id, there is no record. I am not sure if its PG's bug or I am doing something wrong.

Any one have faced such kind of problem?

Answer: 
The exact problem was there were duplicate rows with same `id`. 

I am not sure how it entered the db as there was primary key concern since the table was created. 

The solution was I had to drop the primary key constraint 

```
alter table users drop constraint users_pkey;

```

Then pulled the duplicate record with that id using.

```
Select * from users where id = 339;

```

Now it showed me around 4-5 rows with same id, deleted those rows and it worked.

I am not sure if there is `primary key constraint` on the column why PG don't show duplicate records, if its bug in `PG` or feature.
Check the database. There is already a duplicate value in the table you want to add an index. Check for null value in the table. Seems like there are multiple rows taking null value in user\_id.

Remove duplicates and you will be able to add the index. Happy Coding :)