sqlite single transaction without foreign key or triggers

Aahz aahz at pythoncraft.com
Wed May 13 03:46:27 CEST 2009


In article <Xns9C09513903E8FrtwfreenetREMOVEcouk at 216.196.109.145>,
Rob Williscroft  <rtw at freenet.co.uk> wrote:
>Aahz wrote in news:guao50$1jv$1 at panix3.panix.com in comp.lang.python:
>> In article <Xns9C08E179B66D8rtwfreenetREMOVEcouk at 216.196.109.145>,
>> Rob Williscroft  <rtw at freenet.co.uk> wrote:
>>>
>>>db.execute( '''
>>>         update "sessions" set "uid" = ?
>>>         where "uid" = ? 
>>>         and exists(
>>>                  select * from "users" where "uid" = ?
>>>           )
>>>    ''',
>>>    (v['uid'],s.SID, v['uid']) 
>>>  )
>> 
>> This will be more efficient if you do "select uid from users".
>
>What will be more efficient ?
>
>Do you mean the "select * ..." or do you want to take the exists 
>sub-query out and put it in a python if ? 

"select uid" will be more efficient than "select *", although I suppose
I could be wrong about that given how little I know about current query
optimizers.
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

"It is easier to optimize correct code than to correct optimized code."
--Bill Harlan



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