Re: Re: DBI SQL Query Question

How exactly is fetchrow_hashref more efficient? From the DBI docs:

Because of the extra work "fetchrow_hashref" and Perl
have to perform, it is not as efficient as
"fetchrow_arrayref" or "fetchrow_array".
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Also, you should not save the reference in an array, you may get bitten later. Also from the DBI docs:

Currently, a new hash reference is returned for each
row.  This will change in the future to return the same
hash ref each time, so don't rely on the current
behaviour.
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If you really need to save all the results in an array of hashes, use selectall_arrayref (this changed recently, selectall_hashref use to be the solution to this, but as of DBI 1.20 it now returns a hashref, not an array). If you want to prepare the statement, that's fine, the selectall_* methods will take a sql string or a statement handle as an argument, or you can use one of the new fetchall_* methods.

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Re: Re: Re: DBI SQL Query Question by ehdonhon (Curate) on Jan 11, 2002 at 23:35 UTC
How exactly is fetchrow_hashref more efficient? I didn't mean to slight anybody, or say that the posted way was bad. Please accept my appologies if it came out that way. You are correct about fetchrow_hashref being less efficient than fetchrow_array. But, the original code is taking the elements of the returned array, copying them into its own array, then creating a hash and copying the array into the hash element by element. I can't imagine that is faster than fetchrow_hashref (though I haven't benchmarked it, so maybe it is). It also is less maintainable later if the requirements from the database change since it requires modifying code in more locations. But I suppose that really doesn't have to much to do with execution efficency. Also, you should not save the reference in an array, you may get bitten later. Thanks. That's why I like this place, you learn something new every day.	[reply]

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Re: Re: Re: DBI SQL Query Question
by ehdonhon (Curate) on Jan 11, 2002 at 23:35 UTC

How exactly is fetchrow_hashref more efficient?

I didn't mean to slight anybody, or say that the posted way was bad. Please accept my appologies if it came out that way.

You are correct about fetchrow_hashref being less efficient than fetchrow_array. But, the original code is taking the elements of the returned array, copying them into its own array, then creating a hash and copying the array into the hash element by element. I can't imagine that is faster than fetchrow_hashref (though I haven't benchmarked it, so maybe it is).

It also is less maintainable later if the requirements from the database change since it requires modifying code in more locations. But I suppose that really doesn't have to much to do with execution efficency.

Also, you should not save the reference in an array, you may get bitten later.

Thanks. That's why I like this place, you learn something new every day.

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