Re: sorting/grouping/(non-)unique indexes bug

Unbelievable, but you may have a couple of record with null user_email.

Try:

select * from broken where user_email is null;
select * from reg_user where user_email is null;

Alexey Borzov wrote:
>
> Greetings!
>
> Before I present the following, I must say that 'simple' index
> corruption is highly improbable; the server did not suffer hard
> reboots.
>
> rdw=# \d reg_user
> Table "reg_user"
> Column | Type | Modifiers
> ------------------+------------------------+------------------------------------------------
> user_id | integer | not null default nextval('reg_user_seq'::text)
> user_email | character varying(50) | not null
> user_passwd | character varying(32) | not null
> user_active | boolean | not null default 't'
> user_allow_pauth | boolean | default 'f'
> user_full_name | character varying(100) |
> user_pseudonym | character varying(100) |
> user_who | character(1) |
> Primary key: reg_user_pkey
> Unique keys: reg_user_email_key
>
> rdw=# \d reg_user_email_key
> Index "reg_user_email_key"
> Column | Type
> ------------+-----------------------
> user_email | character varying(50)
> unique btree
>
> rdw=# create table broken as select user_email from reg_user;
> SELECT
>
> rdw=# -- one may think that emails are unique...
> rdw=# select count(user_email) from broken;
> count
> --------
> 212400
> (1 row)
>
> rdw=# select count(distinct user_email) from broken;
> count
> --------
> 212397
> (1 row)
>
> rdw=# -- look closely at the numbers
> rdw=# select user_email, count(user_email) from broken group by user_email order by 2 desc;
> user_email | count
> ----------------------------------------------------+-------
> [duplicated email] | 2
> [some email] | 1
> [some email] | 1
> [some email] | 1
>
> rdw=# delete from broken where user_email = '[duplicated email]';
> DELETE 2
>
> rdw=# select user_email, count(user_email) from broken group by user_email order by 2 desc;
> user_email | count
> ----------------------------------------------------+-------
> [another email] | 2
> [some email] | 1
> [some email] | 1
>
> rdw=# delete from broken where user_email = '[another email]';
> DELETE 2
>
> rdw=# select user_email, count(user_email) from broken group by user_email order by 2 desc;
> user_email | count
> ----------------------------------------------------+-------
> [some email] | 1
> [some email] | 1
> [some email] | 1
>
> rdw=# --finally, no more duplicates!
> rdw=# create unique index broken_email_key on broken (user_email);
> ERROR: Cannot create unique index. Table contains non-unique values
>
> rdw=# select version();
> version
> -------------------------------------------------------------
> PostgreSQL 7.2.1 on i686-pc-linux-gnu, compiled by GCC 2.96
> (1 row)
>
> $psql -l
> List of databases
> Name | Owner | Encoding
> -----------+----------+-----------
> ...
> rdw | alex | WIN
> ...
>
> The server is run under ru_RU.CP1251 locale, initdb was done under the
> same locale.
>
> As you probably guessed, reg_user table contains actual email
> addresses of our site's registered users. I can provide them for
> testing (without passwords and stuff, of course) if this is going to
> help.
>
> --
> Yours, Alexey V. Borzov, Webmaster of RDW.ru
>
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