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All the Perl that's Practical to Extract and Report

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  • A wise man said any SQL query without an ORDER BY clause is a stealth bug waiting to emerge when the implicit order dependency explodes into view.

    In the customer-visit itinerary, ORDER BY may actually be a better solution than DISTINCT -- the repetition value in the BAG will be needed to help plan how long to lay over in each city, as it measures how many visits are required there. GROUP BY (City) COUNT(Customer) might be better, and would get you the equivalent of DISTINCT.

    # I had a sig when sigs were cool
    use Sig;
    • If you need to know counts that's what "GROUP BY" is for, so we can do:
      SELECT city, COUNT(customer_id) as customer_count
        FROM Customer
      GROUP BY city
      ORDER BY city
      This will have no dupes and gives you the same numerical information as a dupe-containing result, but in a nice sane way, with no need to count dupes programatically in the program that executes that query.