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Java daemon

 
 
Arved Sandstrom
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      11-20-2012
On 11/19/2012 09:22 PM, Arne Vajhøj wrote:
> On 11/19/2012 7:38 PM, Arved Sandstrom wrote:
>> On 11/18/2012 09:41 PM, Arne Vajhøj wrote:
>>> On 11/18/2012 8:05 PM, Martin Gregorie wrote:
>>>> On Sun, 18 Nov 2012 16:43:39 -0500, Arne Vajhøj wrote:
>>>>> And most of the non-standard SQL problems went away with MySQL 4.1 and
>>>>> 5.0 back in 2005 and 2006.
>>>>>
>>>> So, you're telling me its now ditched auto-incrementing fields and has
>>>> implemented sequences?
>>>
>>> No.
>>>
>>> But then auto increment is also the standard (with IDENTITY
>>> keyword though).
>>>
>>> And it is also the most widely supported: MySQL,
>>> SQLServer, DB2 etc..

>>
>> Oracle has sequences, PostgreSQL has sequences, SQL Server has sequences
>> (now),

>
> In 2012. They have had identity auto increment since it was called
> Sybase.


Hence my "(now)".

>> DB2 has sequences...MySQL, I don't think so (I stand to be
>> corrected).
>>
>>> PostgreSQL has it in the form of SERIAL (even though it is just
>>> syntactic sugar for a sequence).
>>>
>>> Sequences is really an Oracle and PostgreSQL proprietary thing.

>>
>> Not anymore. Sequences were introduced into the SQL standard in 2003. As
>> you alluded to above, this version introduced identity columns (which
>> are considered to use an internal sequence generator).

>
> ????
>
> SQL IDENTITY columns are used the same way as MySQL auto increment
> not the same way as sequences in Oracle and PostgreSQL.
>
> There must be something like a sequence behind it. But if it is not
> visible and the usage is restricted to the auto increment way, then
> that is implementation.
>
> Arne
>

Hence my wording "are considered to". IOW, the spec says that for
definitional purposes, identity columns are associated with an internal
sequence generator.

But it's separate from implementation details - the "notion" of an
internal sequence generator ("notion" being a word used in the spec) is
inherent in the definition of identity columns in the *specification*.
It is simply a useful abstraction, especially seeing as how sequences
were introduced in the same spec. There are both external SGs (the ones
we can create and configure) and internal SGs, the latter being
components of another schema object.

I think we all understand the difference between IDENTITY and (external)
sequences (the latter a la PostgreSQL or Oracle). One is inextricably
associated with a specific table, one is not.

AHS
 
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