fetchrow_array return value

Notromda has asked for the wisdom of the Perl Monks concerning the following question:

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Re: fetchrow_array return value by mpeppler (Vicar) on Jan 10, 2004 at 00:05 UTC
If you use `fetchrow_array()` like that then if there are one or more rows returned then the first one is lost, because you threw it away in the `if()`. Why not do something like: `my $found = 0; while(my @row = $sth->fetchrow_array) { ++$found; ... process @row ... } if(!$found) { ... no rows found ... }` [download] As for using `$sth->rows()`, the problem is that for most database engines the number of rows affected by a SELECT query can only be determined once all of the rows have been fetched... Michael	[reply] [d/l] [select]
Re: fetchrow_array return value by exussum0 (Vicar) on Jan 10, 2004 at 00:46 UTC
my fave is to have an array for results, populate it. If the array has 0 array elements in it, return as if no rows returned, or continue as such. `my @x = (); while( my @arr = fetchrow_array() ) { push(@x, \@arr ); } if( $#x == .... ) else ....` [download] Not compilable in this form, but it's an idea. Play that funky music white boy..	[reply] [d/l]
Re: fethrow_array return value by zby (Vicar) on Jan 09, 2004 at 23:37 UTC
I don't see any problem with that code if only you change the plural form in the comments to singular. You fetch there only one row, not an array of rows, but a list representing a row. From the DBI documentation: `If there are no more rows or if an error occurs, then "fetchrow_array" returns an empty list. You should check "$sth->err" afterwards (or use the "RaiseError" attribute) to discover if the empty list returned was due to an error.` [download] Restating it: the empty list in result means no rows were selected or there was an error.	[reply] [d/l]
Re: Re: fethrow_array return value by Notromda (Pilgrim) on Jan 10, 2004 at 00:17 UTC
In the case in question, there was no need to get the actual data, the only question was if there were any rows returned. Also, does an empty list always evaluate to false? I guess it should... I'm just confused because it appears that this evaluation is not always doing what I expect. Maybe the problem lies elsewhere....	[reply]
Re: Re: Re: fethrow_array return value by Roger (Parson) on Jan 10, 2004 at 01:03 UTC
In the case in question, there was no need to get the actual data, the only question was if there were any rows returned. In that case you could do with a different approach - `my $sql = "SELECT count(*) FROM table WHERE .... "; ...` [download] This query will return a single row containing the count of matching rows (row count) in the table. I believe this is the most efficient and portable way to determine the number of rows, and the fastest too.	[reply] [d/l]
Re: Re: Re: Re: fethrow_array return value by runrig (Abbot) on Jan 10, 2004 at 02:13 UTC
Re: Re: Re: Re: Re: fethrow_array return value by Roger (Parson) on Jan 10, 2004 at 03:05 UTC
returns an empty list, oh my (was: Re: Re: Re: fethrow_array return value) by ysth (Canon) on Jan 11, 2004 at 06:07 UTC
Also, does an empty list always evaluate to false? I am delighted at finding myself inconsistent! I feel passionately that "returns an array" is bad documentation, but "returns an empty list" doesn't make me blink twice, even though from a language-semantics point of view, a routine in scalar context cannnot return an empty list, and `return ()` will in fact be an undef result (and hence false). Do any others find their brains working this way? Or would everyone else consider "returns an array" and "returns an empty list" equally good or bad?	[reply] [d/l]


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