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]

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