I think the OP and us may be way overthinking the OP's problem.
first.pl and second.pl will create temp table schema and each will run a huge query that loads data into respective temp table schema. third.pl will join the two temp tables from first and second and load it into third.

It could very well be that the OP just needs to log onto a network SQL DB and run just 3 SQL commands!?

I am not sure at all there needs to be 4 Perl programs for this!

It appears that a single Perl program of a couple of pages long will do what the OP is requesting. If not, then I want to know why not? (that's a question for the OP).

In reply to Re^2: designing a program - your wisdom needed by Marshall
in thread designing a program - your wisdom needed by SpaceCowboy

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.