| 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 |
| Message-ID: | 49D25673.20406@emproshunts.com |
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| Lists: | pgsql-general pgsql-hackers |
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Greg Stark wrote:
<blockquote
cite="mid:4136ffa0903311006v15eb3a25xf3fa94a8ca089fd6(at)mail(dot)gmail(dot)com"
type="cite">
<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"><justin(at)emproshunts(dot)com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">But consider this fails also
select string_to_array('1, , 3', ',' )::int[] => ERROR: invalid input
syntax for integer: " "
yet this works
select string_to_array('1, 2, 3',',')::int[]
</pre>
</blockquote>
<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
code.
</pre>
</blockquote>
<br>
I disagree. Casting a string to something else can be a very error
prone to begin with. <br>
Having string_to_array() to deal with that possibility is out of its
scope IMHO.<br>
<br>
Consider this. I have intelligent part numbers that need to be split
apart to simplify searching and do math with. <br>
<br>
string_to_array(' F-2500-50 ', '-' ) ::int[]<br>
<br>
Still fails with an error as expected. what is the difference between
' ' and 'F' <br>
<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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