Re: char(0)

2011-10-17 14:28 keltezéssel, Susanne Ebrecht írta:
> On 17.10.2011 10:30, Simon Riggs wrote:
>> On Mon, Oct 17, 2011 at 8:31 AM, Susanne Ebrecht
>> <susanne@2ndquadrant.com> wrote:
>>
>>> PostgreSQL isn't supporting CHAR(0).
>> What does the SQL Standard say?
>>
>
> Document: 02-Foundation
>
> Section: 4.2.1 Introduction to character strings
>
> Begin quoting
> A character string is a sequence of characters. All the characters in a character string
> are taken from a single
> character set. A character string has a length, which is the number of characters in the
> sequence. The length is
> 0 (zero) or a positive integer.
> End quoting

I am looking at 6WD2_02_Foundation_2007-12.pdf.
Search for "<character length>" that is used in section "6.1 <data type>":

<character length> := <unsigned integer> [ <char length units> ]

Section 6.1 doesn't talk about limiting the definition to > 0 values

But in page 157, section "5.3 <literal>":

============================================================
17) The declared type of a <character string literal> is fixed-length character string.
The length of a <character
string literal> is the number of <character representation>s that it contains. Each <quote
symbol> contained
in <character string literal> represents a single <quote> in both the value and the length
of the <character
string literal>. The two <quote>s contained in a <quote symbol> shall not be separated by
any <separator>.

NOTE 92 — <character string literal>s are allowed to be zero-length strings (i.e., to
contain no characters) even though it is
not permitted to declare a <data type> that is CHARACTER with <character length> 0 (zero).
============================================================

So, a table column is not allowed to be char(0) or varchar(0). It's explicit in NOTE 92.

Best regards,
Zoltán Böszörményi

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Zoltán Böszörményi
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