John R Pierce wrote:
> Elian Laura wrote:
>> i understand, but why my teacher wrote in his paper.."Probably the
>> most obvious case is a database engine where the user defines, at run
>> time, if a field is integer, char, float, etc. but, it is not
>> necessary to compile the program again. All this felxibility must be
>> ........."
I am not a PostgreSQL developer but I think the thing to understand here
is that there are two stages involved. If I say much more I think I'll
be guilty of doing your homework for you, I suggest that you look very
carefully at the examples John gave you earlier and consider that from
the viewpoint of the database engine they are being entered at runtime.
>>> CREATE TABLE users (uid INTEGER, username TEXT, firstname TEXT,
>>> lastname TEXT);
>>>
>>> INSERT INTO users (uid, username) VALUES (103, 'jpierce', 'John',
>>> 'Pierce'), ('104', 'elaura', 'Elian', 'Laura');
>>>
>>> SELECT username,firstname,lastname FROM users WHERE uid=103;
If you think about it one of those statements is giving the system
information which it can store (I'm not sure the way it does this is
really important) and re-use.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]