Joe Pluta skrev den 03-09-2007 18:19:

Anyway, as long as you keep your pointer into the index, it's child's play
to run back and forth through the file. And searching the index is just a
simple b-tree lookup, so for even a billion record file you could find a
record in a maximum of about 30 accesses (plus one to read the actual data
record). That's how ISAM works, and that's why it's been so beneficial to
the business community. Add the single store of the System i, and you've
got virtually instant access to often-used files.
Have I understood this correctly? You describe that using ISAM you can navigate the index file very easily - does that lock you in advance to using THIS particular index file and no others?

The major advantage of SQL in a long term setting is that is is disconnected from the actual database tables and indexes, and it does what is necessary to get the job done.


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