Thanks - Re: low cardinality column

Thanks, Rod, Josh and Bill, That' fantastic.

have a nice day,
rong :-)

> Rod Taylor wrote:
>> On Thu, 2003-10-02 at 14:30, Rong Wu wrote:
>>
>>>Hi,
>>>
>>>I have a select like this:
>>>
>>>SELECT MAX(transactionid) FROM cbntransaction WHERE transactiontypeid=0;
>>
>>
>> For various reasons (primarily MVCC and the ability to make custom
>> aggregates making it difficult)  MAX() is not optimized in this fashion.
>>
>> Try:
>>
>>   SELECT transactionid
>>     FROM ...
>>    WHERE ...
>> ORDER BY transactionid DESC
>>    LIMIT 1;
>
> Despite this good suggestion, if you're using this technique to generate
> the next transaction ID, you're going to have errors as concurrency rises.
>
> Use a SERIAL, which guarantees that you won't have two processes generate
> the same number.
>
> --
> Bill Moran
> Potential Technologies
> http://www.potentialtech.com
>
>