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Re: string_to_array with empty input

From: justin <justin(at)emproshunts(dot)com>
To: Greg Stark <stark(at)enterprisedb(dot)com>
Cc: Sam Mason <sam(at)samason(dot)me(dot)uk>, pgsql-general(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org
Subject: Re: string_to_array with empty input
Date: 2009-03-31 17:44:19
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Greg Stark wrote:
  <pre wrap="">On Tue, Mar 31, 2009 at 5:48 PM, justin <a class="moz-txt-link-rfc2396E" href="mailto:justin(at)emproshunts(dot)com">&lt;justin(at)emproshunts(dot)com&gt;</a> wrote:
  <blockquote type="cite">
    <pre wrap="">But consider &nbsp;this fails also

select string_to_array('1, , 3', ',' )::int[] =&gt; ERROR: &nbsp;invalid input
syntax for integer: " "

yet this works

select string_to_array('1, 2, 3',',')::int[]
  <pre wrap=""><!---->

Sure, and the analogous pair string_to_array(' ',',')::int[] and
string_to_array('1 ',',')::int[] behave similarly.

The point is that '' could represent no items or one empty string. We
get to pick which one and in any use case where the string was a list
of objects it's almost certainly intended to be an empty list. And
databases are almost always processing lists of things.

I think the only use case where you want it to be a singleton list of
an empty string is when you're doing string parsing such as building a
lexer or something like that, which is isn't a typical use for sql
I disagree.&nbsp;&nbsp; Casting a string to something else can be a very error
prone to begin with. <br>
Having&nbsp; string_to_array() to deal with that possibility&nbsp; is out of its
scope IMHO.<br>
Consider this.&nbsp; I have intelligent part numbers&nbsp; that need to be split
apart to simplify searching&nbsp; and do math with. <br>
string_to_array(' F-2500-50 ', '-' ) ::int[]<br>
Still fails with an error as expected.&nbsp; what is the difference between
' '&nbsp; and 'F'&nbsp; <br>
So before doing any thing a test needs to be done to verify the
contents, so it can be casted to something else.<br>

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