OpenEuphoria

Re: database theory

• Posted by Daniel Berstein <daber at PAIR.COM> Nov 22, 1998
• 636 views

>Yes, but how would you know to seek the third one?  Let me think.  Well,
>here.  How fast is this?

>sequence last_name
>last_name = ""
>while last_name != "Jordan" -- the name I'm trying to retrieve
>    counter = 1
>    seek(database,counter) -- database is an open file
>    line = gets(database) -- line is a sequence
>    index = find(',',line)
>    last_name = line[1..index-1]
>    counter = counter+80 -- line length, suppose
>end while

>Is this solution viable?  Is there a better way if I can use the "easy" way
>you describe?  Thanks.

No. You're a bit confused. Suppose you records are 100 bytes long, so to
read a record you do:

sequence record
integer i, fn, offset, counter

counter = 1
fn = open("database.dat","rb") -- Note that you must open the file as binary

while record != something do
    seek(fn, 100 * (counter-1))
    for i = 1 to 100 do    -- Read 100 consecutive bytes from file
        record = record & getc(fn)
    end for

    counter = counter+1
end while

This kind of searching is called secuential because you start from the first
record until you find what you where looking for. Once you've understand
this you can start experimenting with more sophisticated searching
algorithms (external indexes, binary search, binary trees, hash tables,
etc.).

Regards,
    Daniel   Berstein
    daber at pair.com