[yunqa.de] Re: disadvantage of using ROWID as the primary key of a table?
- From: Edwin Yip <edwin.yip@xxxxxxxxxxxxxxxxxx>
- To: yunqa@xxxxxxxxxxxxx
- Date: Sat, 25 Jul 2009 00:09:15 +0000
Ralf,
excellent support, thanks.
On 7/24/09, Delphi Inspiration <delphi@xxxxxxxx> wrote:
> At 09:18 24.07.2009, Edwin Yip wrote:
>
>>Thanks for the detailed explanation. so in other words, if I define a
>> column of any name of type "INTEGER PRIMARY KEY", referencing that column
>> in SQL is exactly the same as referencing ROWID, and the values in that
>> column will not be altered unexpected by the engine, right?
>
> Right.
>
>>And Is "INTEGER NOT NULL PRIMARY KEY" equal to "INTEGER PRIMARY KEY"?
>
> Yes.
>
> Regarding null values in ROWIDs, please keep this in mind as well (quoted
> again from the DISQLite3 Help -> SQL Syntax -> CREATE TABLE):
>
> The PRIMARY KEY attribute normally creates a UNIQUE index on the column or
> columns that are specified as the PRIMARY KEY. The only exception to this
> behavior is special INTEGER PRIMARY KEY column, described below. According
> to the SQL standard, PRIMARY KEY should imply NOT NULL. Unfortunately, due
> to a long-standing coding oversight, this is not the case in SQLite. SQLite
> allows NULL values in a PRIMARY KEY column. We could change SQLite to
> conform to the standard (and we might do so in the future), but by the time
> the oversight was discovered, SQLite was in such wide use that we feared
> breaking legacy code if we fixed the problem. So for now we have chosen to
> continue allowing NULLs in PRIMARY KEY columns. Developers should be aware,
> however, that we may change SQLite to conform to the SQL standard in future
> and should design new programs accordingly.
>
> Ralf
>
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>
--
Best Regards,
Edwin Yip
Mind Mapping is as Effortless as Typing
http://www.InnovationGear.com
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