Orchid XP v8 wrote:

> 
> The concept of performing a multi-table join where the tables are all 
> stored on magnetic tape scares me. o_O
> 
> My God, it could take months...
> 

Not at all.  Simply sort the two (or more) files in sequence by the join 
key (one or more fields).  Then it is a matched scan or 'merge join' 
through both.  Variants for Inner, Left, Right and Full Outer joins.

As to sorting large tape files - You already have my reminiscence of 
'Real Sort I' on your blog.  Actually that whole thing was equivalent to 
a join of the account table to the transaction table when both were 
stored as sequential files on multiple volumes of tape.  Multiple months 
of Tran had to be merged and sorted into account sequence.

This was before disk databases and SQL were practical considerations for 
this application.

Back then (circa 1984) the bank that I worked for might have had about 
40 disk drives.  Each the size of a washing machine.  They were IBM 3350 
DASD providing about 300Mb capacity each - so long as you chose an 
efficient block size for the record length.

So that was about 12Gb of disk in total - for a largish bank.  In my 
pocket I now carry a 16Gb memory stick to backup files and sync across 
machines.

Tapes back then held something like 100Mb per reel (IBM 3420 1200 foot 
?) reel.  But there could be thousands of tapes in the library so that 
was hundreds of Gb.

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