Обсуждение: Empty Output? How Do I Determine the Character?

I cannot determine what character is stored in a varchar...

For instance:
thedonnaholics=# select state from mailing_list where rec_num = 7;
 state
-------

(1 row)

If I then execute:
thedonnaholics=# select count(*) from mailing_list where state = '';
 count
-------
     0
(1 row)

So, what is in that first row?

This also returns 0:
thedonnaholics=# select count(*) from mailing_list where state = ' ';
 count
-------
     0
(1 row)

Any ideas? I'd like to select all rows that contain whatever that first one
contains...

Hunter

Hunter Hillegas <lists@lastonepicked.com> writes:
> I cannot determine what character is stored in a varchar...
> For instance:
> thedonnaholics=# select state from mailing_list where rec_num = 7;
>  state
> -------

> (1 row)

I'd say it's either NULL or between one and five space characters.
To find out, try something like

select '>' || state || '<' from mailing_list where rec_num = 7;

            regards, tom lane

Ok... I don't think that it is null:
thedonnaholics=# select count(*) from mailing_list where state = null;
 count
-------
     0
(1 row)

I ran the query you suggested but I don't know what it means:
thedonnaholics=# select '>' || state || '<' from mailing_list where rec_num
= 7;
 ?column?
----------

(1 row)

Any insight appreciated.

Thanks,
Hunter

> From: Tom Lane <tgl@sss.pgh.pa.us>
> Date: Fri, 08 Aug 2003 19:03:24 -0400
> To: Hunter Hillegas <lists@lastonepicked.com>
> Cc: PostgreSQL <pgsql-general@postgresql.org>
> Subject: Re: [GENERAL] Empty Output? How Do I Determine the Character?
>
> Hunter Hillegas <lists@lastonepicked.com> writes:
>> I cannot determine what character is stored in a varchar...
>> For instance:
>> thedonnaholics=# select state from mailing_list where rec_num = 7;
>>  state
>> -------
>
>> (1 row)
>
> I'd say it's either NULL or between one and five space characters.
> To find out, try something like
>
> select '>' || state || '<' from mailing_list where rec_num = 7;
>
> regards, tom lane

Hunter Hillegas <lists@lastonepicked.com> writes:
> I ran the query you suggested but I don't know what it means:
> thedonnaholics=# select '>' || state || '<' from mailing_list where rec_num
> = 7;
>  ?column?
> ----------

> (1 row)

It means it's NULL.  (Hint: foo = NULL is not the same as foo IS NULL.)

            regards, tom lane