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Re: multiple open handles to mysql? (loops: fetches within fetches)

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On 12/14/14, 11:57 PM, Jerry Stuckle wrote:
> On 12/14/2014 11:24 PM, Richard Damon wrote:
>> On 12/14/14, 10:47 PM, Jerry Stuckle wrote:
>>> On 12/14/2014 9:54 PM, Richard Damon wrote:
>>>>
>>>> I have used successfully something like
>>>>
>>>> $seth01 = ...
>>>> while($row1 = $seth01->fetch()) {
>>>>     $seth02 = ... /* Build a 2nd query based on the results */
>>>>     while($row2 = $seth02->fetch()) {
>>>>       /* ... */
>>>>     }
>>>> }
>>>>
>>>>
>>>
>>> Which could mean a lot of calls to MySQL, causing a lot of overhead.
>>> Couldn't you have returned everything in one call to MySQL by using the
>>> appropriate JOINs?
>>>
>>
>> In my case the second query is to a different database, so a JOIN
>> wouldn't work.
>>
>
> Depending on the database, it might - MySQL will do it, for instance.

Even if they use different credentials to access (and physically on 
different servers)?

>
>> It is also possible that the relationship between the queries is too
>> complicated to express in SQL (for example, you need to deserialize a
>> value to get part of the second query.
>>
>
> Ah, then you've got a database design problem.  It fails first normal
> form because you have more than one value in a row/column (a serialized
> field).

Sometimes getting something to "work" is more important than to by 
"correct" by some theoretical standard. Some things get very hard to 
"properly" normalize, and if you did, you make your normal access 
unnecessarily slow.

For example, how would you reasonably normalize a database where the 
"value" of a field is a polymorphic object (that implements some 
interface), whose type might not be know when you write your code?

>
>> Also, in my case each query only generated a few results, so it wasn't
>> worth spending time to optimize things.
>
> That's good for now, but what about later?
>

Sounds like you are advocating premature optimization. Sometimes adding 
a feature means doing thing in non-ideal manners, to avoid the need of 
an extensive re-write now. Yes, at some point later it might end up 
being required, but at that point the needs might be different so the 
rewrite would be different than if I did it now.

If I did something like this in a new design, there might be more 
justification of a complaint.

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multiple open handles to mysql? (loops: fetches within fetches) oldyork90@yahoo.com - 2014-12-10 21:25 -0800
  Re: multiple open handles to mysql? (loops: fetches within fetches) Jerry Stuckle <jstucklex@attglobal.net> - 2014-12-11 22:45 -0500
    Re: multiple open handles to mysql? (loops: fetches within fetches) "J.O. Aho" <user@example.net> - 2014-12-12 07:51 +0100
      Re: multiple open handles to mysql? (loops: fetches within fetches) Jerry Stuckle <jstucklex@attglobal.net> - 2014-12-12 09:59 -0500
  Re: multiple open handles to mysql? (loops: fetches within fetches) oldyork90@yahoo.com - 2014-12-14 14:49 -0800
    Re: multiple open handles to mysql? (loops: fetches within fetches) Jerry Stuckle <jstucklex@attglobal.net> - 2014-12-14 19:49 -0500
  Re: multiple open handles to mysql? (loops: fetches within fetches) Richard Damon <Richard@Damon-Family.org> - 2014-12-14 21:54 -0500
    Re: multiple open handles to mysql? (loops: fetches within fetches) Jerry Stuckle <jstucklex@attglobal.net> - 2014-12-14 22:47 -0500
      Re: multiple open handles to mysql? (loops: fetches within fetches) Richard Damon <Richard@Damon-Family.org> - 2014-12-14 23:24 -0500
        Re: multiple open handles to mysql? (loops: fetches within fetches) Jerry Stuckle <jstucklex@attglobal.net> - 2014-12-14 23:57 -0500
          Re: multiple open handles to mysql? (loops: fetches within fetches) Richard Damon <Richard@Damon-Family.org> - 2014-12-19 08:50 -0500
            Re: multiple open handles to mysql? (loops: fetches within fetches) Jerry Stuckle <jstucklex@attglobal.net> - 2014-12-19 11:07 -0500
              Re: multiple open handles to mysql? (loops: fetches within fetches) Richard Damon <Richard@Damon-Family.org> - 2014-12-20 14:51 -0500
                Re: multiple open handles to mysql? (loops: fetches within fetches) Jerry Stuckle <jstucklex@attglobal.net> - 2014-12-20 15:50 -0500

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