[thelist] Sessions in PHP4

Liz Lawson lizlawson at charitycards.co.uk
Wed Jul 26 03:31:41 CDT 2000


>> ... mysql offers a LAST_INSERT_ID function (as in SELECT
>> LAST_INSERT_ID FROM table_whatever), which returns the
>> last value automatically generated for an AUTO_INCREMENT
>> field, so you could retrieve the primary key for the first insert that
>way.

......snip........

>on the other hand, i wonder if it's all that efficient, i mean, it's
>[almost] the same as select max(id)
>


nope....LAST_INSERT_ID gets the last ID inserted by the thread that calls
it, while select max(id)
gets the maxium value, which means that if thread B did an insert between
thread A inserting and getting the
max(id), thread A would have the wrong ID....remember, mysql doesn't have
(production-safe) transactions, so
without LAST_INSERT_ID you'd have to explicitly lock the table to ensure you
got the correct Id back.



Liz






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